ISSN: 0256-307X 中国物理快报 Chinese Physics Letters

Volume 30 Number 7 July 2013 A Series Journal of the Chinese Physical Society Distributed by IOP Publishing Online: http://iopscience.iop.org/0256-307X http://cpl.iphy.ac.cn

C HINESE P HYSICAL S OCIET Y

Institute of Physics PUBLISHING CHIN. PHYS. LETT. Vol. 30, No. 7 (2013) 077102

* A Density Functional Study of the Gold Cages MAu16 (M = Si, Ge, and Sn)

TANG Chun-Mei(唐春梅)**, ZHU Wei-Hua(朱卫华), ZHANG Ai-Mei(张爱梅), ZHANG Kai-Xiao(张开骁), LIU Ming-Yi(刘明熠) College of Science, Hohai University, Nanjing 210098

(Received 20 March 2013)

Relativistic density functional calculations are performed to explore the promise of MAu16(M=Si, Ge, and Sn) clusters as magic clusters and building blocks in developing cluster-assembled materials. C1 and Cs, two isomers of SiAu16, GeAu16 and SnAu16 with M (Ge or Sn) at the center of the cage, named, respectively, as SiAu16–C1, SiAu16–Cs, GeAu16-center, and SnAu16-center, are calculated to be the most stable. The Au–M bond should have both ionic and covalent characteristics. Their static linear polarizabilities and first-order hyperpolarizabilities are found to be sensitive to the delocalization of the valence electrons of the M atom, as well as their structures and shapes.

PACS: 71.20.Be, 31.15.xw, 36.40.Cg DOI: 10.1088/0256-307X/30/7/077102

− Au16 is a hollow cage with a slightly distorted sets including 푑 polarization functions (DNP) that are ** tetrahedral (Td) symmetry, and has a sufficiently large comparable to Gaussian 6-31G basis sets. Relativis- [1] − internal volume. The diameter of the Au16 cage is tic calculations are performed with scalar relativistic about 5.5 Å, suggesting possible endohedral doping to corrections to valence orbitals relevant to the atomic form a new class of gold cages with tailored proper- bonding properties via a local pseudopotential.[13] ties similar to endohedral fullerenes.[2] There is much The electronic structures are obtained by solving the − [14] research on Au16 clusters doped by many kinds of Kohn–Sham (KS) equations self-consistently. Nat- atoms.[3−5] Common to these previous studies is the ural bonding orbital (NBO) analyses are made to compliance to the electron counting rule,[6] a key fac- obtain the effective charges on each atom, and the tor in the high stability of gold-based clusters. self-consistent field procedures are carried out witha Recently, Wang et al.[7] reported on the photoelec- convergence criterion of 106 a.u. on the energy and tron spectra (PES) and theoretical studies of doping a electron densities. Geometry optimizations are per- − group IV atom into the Au16 cage, and found that the formed by the Broyden–Fletcher–Goldfarb–Shanno dopant atom was exohedral (Ge, Sn) or became part algorithm[15] with a convergence criterion of 103 a.u. 5 of the gold cage (Si), i.e., Cs and C1, two symmetric on the displacement and 10 a.u. on the energy. We − − isomers for SiAu16 and SnAu16, and one Cs isomer confirm the stability of the lowest energy structure as − [8] for GeAu16. Later, Sun et al. discovered that the the minima of the potential energy surface by con- outer surface of the neutral Au16 cage was more reac- sidering vibrational frequency. There is no imaginary tive for Si doping than its interior, similar to the case frequency for the structures reported here. for the gold bulk. In this Letter, we will investigate In this study, first we simply choose the structures [7] the MAu16 (M = Si, Ge, and Sn) clusters, and aim to given by Wang et al. as the initial configurations for answer the following questions. (1) Can the electron the neutral MAu16 (M=Si, Ge, and Sn) and the cor- counting rule be adopted to study the stabilities of responding cationic and anionic structures to explore MAu16 (M = Si, Ge, and Sn)? (2) What are the low- their stabilities. These structures are, respectively, est energy structures of the MAu16 (M = Si, Ge, and signed SiAu16-C1, SiAu16-Cs, GeAu16-Cs, SnAu16-C1, Sn) clusters? (3) What are the electronic properties and SiAu16-Cs. It is found that Si is near two neigh- and polarizabilities of the most stable MAu16 (M = Si, boring triangular facets, while Ge and Sn are outside Ge, and Sn) structures? the center of a four-membered ring in a hexagonal. We 3 [9] We use the DMol program to perform density compare the 퐸g of the five neutral SiAu16-C1, SiAu16- [10] functional theory (DFT) calculations for all the Cs, GeAu16-Cs, SnAu16-C1, and SiAu16-Cs structures, clusters. The Perdue Burke Ernzerh (PBE) of the as well as those of their corresponding cationic and [11] functional, based on the generalized gradient ap- anionic structures. The 퐸g, defined as the energy proximation (GGA)[12] method, is chosen. The ba- gap between the highest occupied molecular orbital sis sets used in this work are double numerical basis (HOMO) and the lowest unoccupied molecular orbital

*Supported by the Qing Lan Project, the National Natural Science Foundation of China under Grant Nos 11104062 and 10947132, the ‘333 High-Level Talent Cultivation Project’ Special Foundation of Jiangsu Province, the China Postdoctoral Science Foundation under Grant No 20100471307, the Jiangsu Planned Projects for Postdoctoral Research Funds under Grant No 1001001C, the Excellent Innovation Personal Support Plan of Hohai University, and the Fundamental Research Funds for the Central Universities under Grant No 2012B12914. **Corresponding author. Email: [email protected] © 2013 Chinese Physical Society and IOP Publishing Ltd 077102-1 CHIN. PHYS. LETT. Vol. 30, No. 7 (2013) 077102

(LUMO), is a useful quantity for examining the ki- gle faces (one is the triangle in a hexagon and the netic stabilities of clusters. A large 퐸g corresponds other is the additional triangle between two neighbor- to the high energy required for electron excitation.[16] ing hexagons). Here, we put the M atom, respec- The calculated 퐸g of the neutral MAu16 (M = Si, Ge, tively, at the center of the cage, inside or outside and Sn) are in agreement with that shown in their of the cage symmetric to two atoms, at the bridge [7] PES. Moreover, the neutral MAu16 (M = Si, Ge, and centers of two kinds of bonds, and at the face cen- + Sn) have larger 퐸g than those of MAu16 (M = Si, Ge, ters of two kinds of faces. Additionally, the C1 or and Sn) and MAu16 (M = Si, Ge, and Sn), indicating Cs isomers for MAu16 (M=Si, Ge, and Sn) proposed [7] that the neutral MAu16 (M = Si, Ge, and Sn) are the by Wang et al. are also taken into consideration. most kinetically stable. This can be understood by Therefore, a total of 14 or 15 different isomers for [4] the jellium model. The clusters with 2, 8, 18, 20, MAu16 (M=Si, Ge, and Sn) are optimized to explore 40, 58,... valence electrons show pronounced intensi- the most stable location for the M. It is found that ties in the mass spectra, and thus they are called magic M at six different sites inside the cage all shift to clusters. According to the electronic configuration of the center cage after optimization, and the C1 and the Au atom, the Au16 cluster should have 16 valence Cs isomers are still the most stable for SiAu16. As electrons considering only the 6푠 electron, and corre- for GeAu16 and SnAu16, the structures with M at the + spondingly, MAu16, MAu16, and MAu16 should have center of the cage have the lowest energy. In order total electrons of 20, 19, and 21, respectively. There- to ensure that the calculated DFT result is reliable, fore, we suggest that the neutral MAu16 (M = Si, Ge, we also perform a global-minimum search for the low- and Sn) are magic clusters and promising as building est energy MAu16 (M=Si, Ge, and Sn) clusters. We blocks in developing novel cluster-assembled materi- employ basin-hopping global-optimization, which has als. Furthermore, removing an electron from MAu16 been previously used to search for low-lying anionic will lead to a significant drop in the stability, result- gold clusters[17] and bimetallic mixed clusters.[18] The ing in a high vertical ionization potential (VIP). To global-minimum search results also confirm the most the contrary, adding an electron to MAu16 will lead stable isomers for MAu16 (M=Si, Ge, and Sn). There- to a small energy release and result in a low vertical fore, Si, Ge, and Sn all prefer to be enclosed inside the electron affinity (VEA). Au16 cage. As we know, the atomic radius of M is in In order to find out the most stable structures for the order Sn>Ge>Si, and thus the Si with the small- MAu16 (M = Si, Ge, and Sn), we next put the M atom est radius can shift more easily to the off-center site, at different sites and take these doped structures into causing the remarkable distortions in the Au16 cage. the calculation. It has been reported that Td-Au16 is However, the Ge and Sn with larger radii can only lo- the smallest gold cage, and has an empty interior with cate at the center of the Au16 cage. Therefore, SiAu16 [9] a diameter of 5.5 Å, four equilateral triangles, and has a different ground-state structure from16 GeAu four regular hexagons. Thus, there are two kinds of and SnAu16. We rename GeAu16-1 and SnAu16-1 as atoms (one is in the hexagon and the other in the GeAu16-center and SnAu16-center. In the following, triangle), two kinds of bonds (one is the radius of we choose the four SiAu16–C1, SiAu16–Cs, GeAu16- the hexagon and the other is the common bond of center, and SnAu16-center structures to explore their a hexagon and a triangle), and two kinds of trian- electronic properties and polarizabilities.

Table 1. The 퐸g, 퐴[Au–Au], Au–M, 퐶M, VIP, VEA, 휒, 휂, and 휔 of Au16, SiAu16–C1, SiAu16–Cs, GeAu16-center, and SnAu16- center.

퐸g (eV) 퐴[Au–Au] (Å) Au–M (Å) CM (e) VIP (eV) VEA (eV) 휒 (eV) 휂 (eV) 휔 (eV) Au16 0.25 2.84 6.22 2.90 4.56 1.66 6.27 SiAu16–C1 1.49 3.00 2.3 −0.72 6.98 2.32 4.65 2.33 4.64 SiAu16–Cs 1.49 2.98 2.41 −0.72 6.58 2.38 4.48 2.10 4.78 GeAu16-center 1.87 2.87 2.62 −0.41 6.50 2.70 4.60 1.90 5.56 SnAu16-center 2.01 2.90 2.81 −0.72 6.40 2.83 4.62 1.79 5.97

Table1 presents the 퐸g, averaged Au–Au bond the recently published results of Ih–W@Au12 (2.84– [20] [21] length(퐴[Au–Au]), and the shortest Au–M bond 2.94Å), Td–Au20 (2.68–3.12 Å), and Ih–Au42 [22] lengths of Au16, SiAu16–C1, SiAu16–Cs, GeAu16– (2.819–2.910 Å). Compared to the calculated av- center, and SnAu16–center. Here, the calculated Au– eraged lengths of all the Au–Au bonds of the Au16 Au averaged bond lengths of SiAu16–C1, SiAu16– cluster, those of the SiAu16–C1, SiAu16–Cs, GeAu16- Cs, GeAu16-center, and SnAu16-center are 2.80 Å, center, and SnAu16-center clusters are elongated 2.80 Å, 2.87 Å, and 3.0 Å respectively, in accor- about 5.6%, 4.9%, 1.1%, 2.1%, respectively, indicating dance with the previous DFT calculations based that the Au16 cages are expanded outwards somewhat, on the local density approximation (2.89 Å) and which is caused by the doped M atom. GGA (2.97 Å).[19] The bond lengths are also close to To further have a clear view of how the M atom

077102-2 CHIN. PHYS. LETT. Vol. 30, No. 7 (2013) 077102 interacts with the Au atom, we next discuss the M– bond should have both ionic and covalent characteris- Au bond length. The shortest M–Au bond lengths tics. are 2.3 Å, 2.41 Å, 2.62 Å, and 2.81 Å for the SiAu16– C1, SiAu16–Cs, GeAu16-center, and SnAu16-center, respectively, shorter than the radii sum of Si and Au, however, slightly longer than the radii sum of M (M = Ge and Sn) and Au. In order to analyze the characters of the Au–M bond, the deformation SiAu16-C1 SiAu16-Cs GeAu16-center SnAu16-center charge densities of SiAu16–C1, SiAu16–Cs, GeAu16- Fig. 1. The deformation charge densities of SiAu16–C1, center, and SnAu16-center are plotted in Fig. 1, and SiAu16–Cs, GeAu16-center, and SnAu16-center. defined as the total charge densities of a cluster with the densities of the isolated atoms subtracted. The It is known from Table 1 that the 퐸g of the neu- blue area indicates electron accumulation when atoms tral Au16 is only 0.25 eV, suggesting that it has an form a cluster. From the figure, we can see that the de- open-shell electronic structure. Two extra electrons formation charge densities distribute not only around would be required to reach a closed-shell 18-electron 2− the M and Au atoms, but also in the intervals of the Au16 ion, which is also born out by a recent theoreti- [8] M–Au bond, showing some covalent characteristics of cal study. The larger 퐸g’s of SiAu16–C1, SiAu16–Cs, the M–Au bonds. In addition, we also perform NBO GeAu16-center, and SnAu16-center indicate that these analyses for SiAu16–C1, SiAu16–Cs, GeAu16-center, four structures have kinetic stabilities comparable to [23] and SnAu16-center. The NBO charges on the M atom C60, which has an 퐸g of 1.66 eV. Therefore, the listed in Table 1 indicate that there is some charge neutral MAu16 (M = Si, Ge, and Sn) are rather sta- transfer from the M to Au atoms, and the M–Au bond ble and promising as fundamental building blocks in has some ionic characteristics. Therefore, the Au–M constructing cluster-assembled materials.

SiAu -C SiAu -C Au16 16 1 16 s GeAu16-center SnAu16-center

HOMO HOMO HOMO HOMO HOMO

LUMO LUMO LUMO LUMO LUMO

Fig. 2. The HOMO and LUMO wavefunctions of SiAu16–C1, SiAu16–Cs, GeAu16-center, and SnAu16-center.

In quantum chemistry, the reactivity of a molecule Table 1 also shows the VIP, VEA, molecular elec- can be correlated with its frontier orbitals. Com- tronegativity (휒), chemical hardness (휂), and elec- monly, the atom that is the main component of the trophilicity index (휔) of Au16, SiAu16–C1, SiAu16– HOMO should have the stronger ability for detach- Cs, GeAu16-center, and SnAu16-center, respectively. ing electrons, whereas the atom that is the main The VIP is the energy difference between the posi- component of the LUMO should be easier to gain tively charged and neutral clusters. The VEA is eval- electrons.[24] We present the HOMO and LUMO wave- uated by adding one electron to the neutral cluster in functions of SiAu16–C1, SiAu16–Cs, GeAu16-center, its equilibrium geometry and taking the difference be- and SnAu16-center in Fig. 2, where the blue and yellow tween their total energies. The 휒 is identified as the represent the negative and positive parts of the wave- negative of the partial derivative of the energy 퐸 of an functions. It is observed from the figure that the HO- atomic or molecular system with respect to the num- MOs and LUMOs of these four structures have small ber of electrons 푁 for a constant external (i.e., due 휕퐸 [25] distributions on the M. Therefore, the HOMOs and to the nuclei) potential 푣, written as 휒 = −( 휕푁 )휈 . LUMOs of MAu16 should have weak abilities for both On the basis of the hard soft acid base (HSAB) prin- gaining and losing electrons. ciple, 휂 is identified as the second derivative ofthe

077102-3 CHIN. PHYS. LETT. Vol. 30, No. 7 (2013) 077102 energy 퐸 with respect to the number of electrons 푁 As pointed out by Geerings et al.,[28] 휒 is a good 1 휕2퐸 [25] measure of the ability of the molecule to attract elec- at fixed external potential, i.e., 휂 = 2 ( 휕푁 2 )휈 . In a finite difference approximation using integer values trons. 휂, a measure for resistance to deformation or for 푁, the expressions of the 휒 can be rewritten as change, is a very important tool to study the stability 푉 퐼푃 −푉 퐸퐴 of molecular systems. The maximum hardness princi- the Mulliken-type formula: 휒 = 2 , while the 휂 can be rewritten as 휂 = 푉 퐼푃 +푉 퐸퐴 .[26] 휔 is defined ple (MHP) states that the minimum energy structure 2 [27] [37] as the square of its electronegativity divided by two has the maximum 휂. Geerings et al. considered 2 times its chemical hardness, that is, 휔 = 휒 .[27] that 휔 measured the second-order energy change of an 2휂 electrophile as it is saturated with electrons.[26]

Table 2. The 훼 tensor, ⟨훼⟩, Δ훼, and 훽0 of Au16, SiAu16–C1, SiAu16–Cs, GeAu16-center, and SnAu16-center with units of a.u.

Au16 SiAu16–C1 SiAu16–Cs GeAu16-center SnAu16-center 훼푥푥 586.10 635.58 636.05 571.88 577.15 훼푦푦 537.76 615.40 615.06 571.78 576.46 훼푧푧 537.78 575.23 575.07 571.32 575.24 ⟨훼⟩ 553.88 608.74 608.73 571.66 576.28 Δ훼 48.33 53.21 53.66 0.51 1.68 훽0 10.91 658.89 641.23 16.01 2.43 √︀ 2 2 2 The calculated VIP of SiAu16–C1, SiAu16–Cs, [(훼푥푥 − 훼푦푦) + (훼푥푥 − 훼푧푧) + (훼푦푦 − 훼푧푧) ]/2, 3 GeAu16-center, and SnAu16-center are larger than 훽0 = 5 (훽푥휇푥 + 훽푦휇푦 + 훽푧휇푧)/휇0, where 훽푖 = those of the magic Ga13M (M = Li, Na, K, and Rb) 훽푖푥푥 + 훽푖푦푦 + 훽푖푧푧, (푖 = 푥, 푦, 푧). clusters, indicating their considerable stabilities. The Table 2 displays the calculated results of 훼 tensor, VEA of these four clusters are slightly larger than ⟨훼⟩, ∆훼, and 훽0 of SiAu16–C1, SiAu16–Cs, GeAu16- the experimental and theoretical values of the anionic center, and SnAu16-center, as well as those of Au16 [8] MAu16 (M = Si, Ge, and Sn). Furthermore, the VIP for comparison. The static linear polarizability rep- and VEA of all the doped structures are larger and resents one of the most important observables for the smaller than those of the pristine Au16, respectively, understanding of the electronic properties of clusters. indicating that the doped M increases the structural It is proportional to the number of electrons of the stabilities. As M progresses from Si to Sn, the VIP systems, and very sensitive to the delocalization of and 푥 of SiAu16–C1, SiAu16–Cs, GeAu16-center, and valence electrons as well as the structure and shape of [30] SnAu16-center decrease, while the VEA, 휂 and 휔 of the system. Obviously, as for Au16, SiAu16-C1, and them increase gradually. SiAu16-Cs, the 훼 components are different in the 푥, 푦, In an even, weak electric field, the total en- and 푧 directions (훼푥푥, 훼푦푦, 훼푧푧), resulting in large ⟨훼⟩ ergy 퐸 of a molecular system in the presence of values. However, GeAu16-center and SnAu16-center a static electric field can be expressed as 퐸 = have almost the same 훼 components, resulting in very 0 1 1 [28] 0 퐸 −휇푖퐹푖− 2 훼푖푗퐹푖퐹푗 − 6 훽푖푗푘퐹푖퐹푗퐹퐾 −· · ·, where 퐸 small ⟨훼⟩ values. As we know, the former Td symme- is the energy of the molecule in the absence of an elec- try is completely destroyed to the C1 or Cs symmetry tronic field, 휇푖 is the component of the dipole moment upon the adsorption of the Si atom on Au16, while it vector, 훼푖푗 is the static linear polarizability tensor, is almost unaffected by the doped Ge and Sn atthe 훽푖푗푘 is the first-order hyperpolarizability tensor, and center of the cage. Thus, the static linear polarizabil- 푖, 푗 and 푘 are the designated different components of ity is indeed very sensitive to the molecular structure, the 푥, 푦, and 푧 directions, respectively. The molecular as Zagorodniy et al. stated.[31] The calculated tensor Hamiltonian includes a term (−휇0퐹¯) describing the components of SiAu16–C1, SiAu16–Cs, GeAu16-center, interaction between the external uniform static field and SnAu16-center are comparable to those of Au16. and the molecule. Here, 휇0 is the molecular total Actually, this is expected since their 푠푝 structure is dipole moment. A set of equations are given by calcu- rich with 푝 bonds delocalized along the entire body of lating the system energy with each electric field, and the system.[30] then the values of 휇푖, 훼푖푗, and 훽푖푗푘 can be obtained As is known, the first-order hyperpolarizability is through simultaneous equations by altering 퐸 with an estimate of the intrinsic molecular hyperpolariz- respect to 퐹 . Apart from the tensor components of ability in the absence of any resonance effect. The the static linear polarizability and first-order hyper- first-order hyperpolarizability 훽0 of C60 is zero, the polarizability, we also consider the mean static linear same as that calculated by Xie et al.[32] This is actu- polarizability ⟨훼⟩, the anisotropy ∆훼 of the polariz- ally expected since they display inversion symmetries. ability tensor, which can be used as a measure of the Consequently, both SiAu16–C1 and SiAu16–Cs have anisotropy of the electron densities of the cluster, and large 훽0 values in contrast to Au16, while the GeAu16- the first-order hyperpolarizability 훽0. These quanti- center and SnAu16-center have very small 훽0 values. [29] ties are defined as: ⟨훼⟩ = [훼푥푥 +훼푦푦 +훼푧푧]/3, ∆훼 = As we know, in the different structures and shapes of

077102-4 CHIN. PHYS. LETT. Vol. 30, No. 7 (2013) 077102

MAu16, the electron distribution of Si is also different 127 214706 from that of Ge and Sn, which can result in different [9] Delley B 1990 J. Chem. Phys. 92 508 static linear polarizabilities and first-order hyperpo- [10] Artacho E, Portal D S, Ordejòn P and Garcl‘a A 1999 Phys. Status Solidi B 215 809 larizabilities under the external field. Therefore, the [11] Pei X Y, Yang X P and Dong J M 2006 Phys. Rev. B 73 delocalization of the valence electrons of the M atom, 195417 [32] as well as the structure and shape of MAu16, are [12] Ding C G, Yang J L, Li Q X, Wang K L and Toigo F 1998 responsible for the large variety in static linear polar- Phys. Lett. A 248 49 [13] Delley B 2002 Phys. Rev. B 66 155125 izability and first-order hyperpolarizability. [14] Lee C, Yang W and Parr R G 1988 Phys. Rev. B 37 785 In summary, neutral MAu16 (M = Si, Ge, and Sn) [15] Fletcher R 1980 Practical Methods of Optimization (New are magic clusters and promising as building blocks York: Wiley) Theor. Chem. Acc. 102 in developing cluster-assembled materials. The M–Au [16] Aihara J I 1999 134 [17] Yoo S and Zeng X C 2005 Angew. Chem. Int. Ed. 44 1491 bond in SiAu16–C1, SiAu16–Cs, GeAu16-center, and [18] Gao Y, Bulusu S and Zeng X C 2005 J. Am. Chem. Soc. SnAu16-center should have both ionic and covalent 127 15680 characteristics. The static linear polarizabilities and [19] Autschbach J, Hess B A, Johansson M P, Neugebauer J, Patzschke M, Pyykk P, Reiher M and Sundholm D 2004 first-order hyperpolarizabilities of SiAu16–C1, SiAu16– Phys. Chem. Chem. Phys. 6 11 Cs, GeAu16-center, and SnAu16-center are found to be [20] Li X, Kiran B, Li J, Zhai H J and Wang L S 2002 Angew. sensitive to the delocalization of the valence electrons Chem. Int. Ed. 114 4980 of the M atom, as well as their structures and shapes. [21] Gao Y and Zeng X C 2005 J. Am. Chem. Soc. 127 3698 [22] Denisenko N I, Troyanov S I, Popov A A, Kuvychko I V, Zemva B, Kemnitz E, Strauss S H and Boltalina O V 2004 J. Am. Chem. Soc. 126 1618 References [23] Han Y K 2006 J. Chem. Phys. 124 024316 [24] Wang J and Han J G 2007 Chem. Phys. 342 253 [1] Bulusu S, Li X, Wang L S and Zeng X C 2006 Proc. Natl. [25] Han X, Zhou S J, Tan Y Z, Wu X, Gao F, Liao Z J, Acad. Sci. USA 103 8326 R B, Feng Y Q, Lu X, Xie S Y and Zheng L S 2008 Angew. [2] Chai Y, Guo T, Jin C, Haufler R E, Chibante L P F, Fure J, Chem. Int. Ed. 47 5340 Wang L and Alford J M, Smalley R E 1991 J. Phys. Chem. [26] Geerings P, Proft F D and Langenaeker W 2003 Chem. Rev. 95 7564 103 1793 [3] Wang L M, Bulusu S, Zhai H J, Zeng X C and Wang L S [27] Smith D W 1998 J. Chem. Soc. Faraday Trans. 94 201 2007 Angew. Chem. Int. Ed. 46 2915 [28] Rollefson G K and Dodgen H W 1944 J. Chem. Phys. 12 [4] Walter M and Hakkinen H 2006 Phys. Chem. Chem. Phys. 107 8 5407 [29] Li R J, Li Z R, Wu D, Hao X Y, Li Y, Wang B Q, Tao F [5] Shinde P P, Yadav B D and Kumar V 2012 J. Mater. Sci. M and Sun C C 2003 Chem. Phys. Lett. 372 893 47 7642 [30] Parr R G, Szentpály L V and Liu S 1999 J. Am. Chem. [6] Pyykk P and Runeberg N 2002 Angew. Chem. Int. Ed. 114 Soc. 121 1922 2278 [31] Zagorodniy K, Taut M and Hermann H 2006 Phys. Rev. A [7] Wang L M, Bulusu S, Huang W, Pal R, Wang L S and Zeng 73 054501 X C 2007 J. Am. Chem. Soc. 129 15136 [32] Xie R H, Bryant G W and Smith V H 2003 Chem. Phys. [8] Sun Q, Wang Q, Chen G and Jena P 2007 J. Chem. Phys. Lett. 368 486

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THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS 071201 Enhanced Electron-Positron Pair Production of a Vacuum in a Strong Laser Pulse Field by Frequency Variation LI Zi-Liang, SANG Hai-Bo, XIE Bai-Song

NUCLEAR PHYSICS 072801 Extraction of Mechanical-Reactivity Influences from Neutron Noise Spectra at the IBR-2 Reactor M. Dima, Yu. Pepelyshev

ATOMIC AND MOLECULAR PHYSICS 073101 Theoretical Calculation of Vector Correlations of the Reaction ′ 2 1 + 1 D ( S)+DS(X Σ )→S( D)+D2 WEI Qiang 073201 The Dynamics of Rubidium Atoms in THz Laser Fields JIA Guang-Rui, ZHAO Yue-Jin, ZHANG Xian-Zhou, LIU Yu-Fang, YU Kun 073202 Effect of Electron Initial Longitudinal Velocity on Low-Energy Structure in Above-Threshold Ionization Spectra WU Ming-Yan, WANG Yan-Lan, LIU Xiao-Jun, LI Wei-Dong, HAO Xiao-Lei, CHEN Jing 073401 Electronic Excitation of H2 by Electron Impact Using Multichannel Static-Exchange-Optical Method WANG Yuan-Cheng, MA Jia, ZHOU Ya-Jun 174 1 3 073402 Observation of Photoassociation Spectra of Ultracold Yb Atoms at S0– P1 Inter-Combination Line LONG Yun, XIONG Zhuan-Xian, ZHANG Xi, ZHANG Meng-Jiao, LU¨ Bao-Long, HE Ling-Xiang 073701 Manipulation of Ions in Microscopic Surface-Electrode Ion Traps WAN Wei, CHEN Liang, WU Hao-Yu, XIE Yi, ZHOU Fei, FENG Mang

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS) 074201 Enhancement of Photodetector Responsivity and Response Speed Using Cascaded-Cavity Structure with Subwavelength Metallic Slit DU Ming-Di, SUN Jun-Qiang, QIN Yi, LIAO Jian-Fei 074202 High Power Quasi-Continuous-Wave Diode-End-Pumped Nd:YAG Slab Amplifier at 1319 nm ZHENG Jian-Kui, BO Yong, XIE Shi-Yong, ZUO Jun-Wei, WANG Peng-Yuan, GUO Ya-Ding, LIU Biao-Long, PENG Qin-Jun, CUI Da-Fu, LEI Wen-Qiang, XU Zu-Yan 074203 Ptychographical Imaging Algorithm with a Single Random Phase Encoding SHI Yi-Shi, WANG Ya-Li, LI Tuo, GAO Qian-Kun, WAN Hao, ZHANG San-Guo, WU Zhi-Bo 074204 Tuning Properties of External Cavity Violet Semiconductor Laser LV Xue-Qin, CHEN Shao-Wei, ZHANG Jiang-Yong, YING Lei-Ying, ZHANG Bao-Ping 074205 End-Output Coupling Efficiency Measurement of Silicon Wire Waveguides Based on Correlated Photon Pair Generation LV Ning, ZHANG Wei, GUO Yuan, ZHOU Qiang, HUANG Yi-Dong, PENG Jiang-De 074206 Gain Improvement of Fiber Parametric Amplifier via the Introduction of Standard Single-Mode Fiber for Phase Matching ZHU Hong-Na, LUO Bin, PAN Wei, YAN Lian-Shan, ZHAO Jian-Peng, WANG Ze-Yong, GAO Xiao-Rong 074207 End-Pumped Slab Yb:YAG Crystal Emitting 1030 nm Laser at Room Temperature XU Liu, ZHANG Heng-Li, MAO Ye-Fei, DENG Bo, HE Jing-Liang, XIN Jian-Guo 074208 Modeling 2D Gyromagnetic Photonic Crystals by Modified FDTD Method LI Qing-Bo, WU Rui-Xin, YANG Yan, SUN Hui-Ling 074209 Phonon Lifetime Measurement by Stimulated Brillouin Scattering Slow Light Technique in Optical Fiber CHEN Wei, MENG Zhou, ZHOU Hui-Juan 074301 Numerical Solution of Range-Dependent Acoustic Propagation QIN Ji-Xing, LUO Wen-Yu, ZHANG Ren-He, -Mei 074302 Modeling of Shock Wave Generated from a Strong Focused Ultrasound Transducer CHEN Tao, QIU Yuan-Yuan, FAN Ting-Bo, ZHANG Dong 074701 Surface Tension Gradients on Mixing Processes after Coalescence of Binary Equal-Sized Droplets LIU Dong, GUO Yin-Cheng, LIN Wen-Yi 074702 An Immersed Boundary-Lattice Boltzmann Simulation of Particle Hydrodynamic Focusing in a Straight Microchannel SUN Dong-Ke, JIANG Di, XIANG Nan, CHEN Ke, NI Zhong-Hua

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES 075201 Observation of Electron Fishbone-Like Instabilities in EAST Heavy Impurity Ohmic Plasma XU Li-Qing, HU Li-Qun, EAST team 075202 A Polymer-Rich Re-deposition Technique for Non-volatile Etching By-products in Reactive Ion Etching Systems A. Limcharoen, C. Pakpum, P. Limsuwan CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

076101 A Band-Gap Energy Model of the Quaternary Alloy InxGayAl1−x−yN using Modified Simplified Coherent Potential Approximation ZHAO Chuan-Zhen,ZHANG Rong, LIU Bin, LI Ming, XIU Xiang-Qian, XIE Zi-Li, ZHENG You-Dou 076102 Low-Dose 1 MeV Electron Irradiation-Induced Enhancement in the Photoluminescence Emission of Ga-Rich InGaN Multiple Quantum Wells ZHANG Xiao-Fu, LI Yu-Dong, GUO Qi, LU Wu 076201 The Anomalous Temperature Effect on the Ductility of Nanocrystalline Cu Films Adhered to Flexible Substrates HU Kun, CAO Zhen-Hua, WANG Lei, SHE Qian-Wei, MENG Xiang-Kang 076202 The Material Behavior and Fracture Mechanism of a Frangible Bullet Composite LI Jian, RONG Ji-Li, ZHANG Yu-Ning, XU Tian-Fu, LI Bin 076401 Harnessing Light and Single Masks to Create Multiple Patterns in a Ternary Blend with Photoinduced Reaction PAN Jun-Xing, ZHANG Jin-Jun, WANG Bao-Feng, WU Hai-Shun, SUN Min-Na 076402 Partial Order in Potts Models on the Generalized Decorated Square Lattice -Pu, CHEN Jing, CHEN Qiao-Ni, XIE Zhi-Yuan, KONG Xin, ZHAO Hui-Hai, Bruce Normand, XIANG Tao

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES 077101 The Structural, Electronic and Elastic Properties, and the Raman Spectra of Orthorhombic CaSnO3 through First Principles Calculations A. Yangthaisong

077102 A Density Functional Study of the Gold Cages MAu16 (M = Si, Ge, and Sn) TANG Chun-Mei, ZHU Wei-Hua, ZHANG Ai-Mei, ZHANG Kai-Xiao, LIU Ming-Yi 077201 Enhanced Performance and Stability in Polymer Photovoltaic Cells Using Ultraviolet-Treated PEDOT:PSS XU Xue-Jian, YANG Li-Ying, TIAN Hui, QIN Wen-Jing, YIN Shou-Gen, ZHANG Fengling 077301 The Effect of Intraband Transitions on the Optical Spectra of Metallic Carbon Nanotubes T. Movlarooy 077302 The Nuclear Dark State under Dynamical Nuclear Polarization YU Hong-Yi, LUO Yu, YAO Wang 077303 Room-Temperature Multi-Peak NDR in nc-Si Quantum-Dot Stacking MOS Structures for Multiple Value Memory and Logic QIAN Xin-Ye, CHEN Kun-Ji, HUANG Jian, WANG Yue-Fei, FANG Zhong-Hui, XU Jun, HUANG Xin-Fan 077304 Quantum Size and Doping Concentration Effects on the Current-Voltage Characteristics in GaN Resonant Tunneling Diodes Hassen Dakhlaoui 077305 The Unconventional Transport Properties of Dirac Fermions in Graphyne LIN Xin, WANG Hai-Long, PAN Hui, XU Huai-Zhe 60 077306 The C–V and G/ω–V Electrical Characteristics of Co γ-Ray Irradiated Al/Si3N4/p-Si (MIS) Structures S. Zeyrek, A. Turan, M. M. B¨ulb¨ul 077307 The Effect of Multiple Interface States and nc-Si Dots in a Nc-Si Floating Gate MOS Structure Measured by their G–V Characteristics , MA Zhong-Yuan, CHEN Kun-Ji, JIANG Xiao-Fan, LI Wei, HUANG Xin-Fan, XU Ling, XU Jun, FENG Duan 077308 Fano-Resonance of a Planar Metamaterial HUANG Wan-Xia 077402 An Insight into the Structural, Electronic and Transport Characteristics of XIn2S4 (X = Zn, Hg) Thiospinels using a Highly Accurate All-Electron FP-LAPW+Lo Method Masood Yousaf, M. A. Saeed, Ahmad Radzi Mat Isa, H. A. Rahnamaye Aliabad, M. R. Sahar

077403 The Optical Study of Single Crystalline Cs0.8(Fe1.05Se)2 with High N´eelTemperature YUAN Rui-Hua, DONG Tao, WANG Nan-Lin 077404 The Finite Temperature Effect on Josephson Junction between an s-Wave Superconductor and an s±-Wave Superconductor WANG Da, LU Hong-Yan, WANG Qiang-Hua 077501 Synthesis and Characterization of Alkaline-Earth Metal (Ca, Sr, and Ba) Doped Nanodimensional LaMnO3 Rare-Earth Manganites Asma Khalid, Saadat Anwar Siddiqi, Affia Aslam 077502 A First-Principles Investigation of the Carrier Doping Effect on the Magnetic Properties of Defective Graphene LEI Shu-Lai, LI Bin, HUANG Jing, LI Qun-Xiang, YANG Jin-Long 0 077503 Room-Temperature d Ferromagnetism in Nitrogen-Doped In2O3 Films SUN Shao-Hua, WU Ping, XING Peng-Fei 077701 Wafer-Scale Flexible Surface Acoustic Wave Devices Based on an AlN/Si Structure ZHANG Cang-Hai, YANG Yi, ZHOU Chang-Jian, SHU Yi, TIAN He, WANG Zhe, XUE Qing-Tang, REN Tian-Ling 077801 Magnetic-Field-Induced Stress-Birefringence in Laminate Composites of Terfenol-D and Polycarbonate LUO Xiao-Bin, WU Dong, ZHANG Ning 077802 The Fano-Like Resonance in Self-Assembled Trimer Clusters ZHANG Mei, LI Liang-Sheng, ZHENG Ning, SHI Qing-Fan

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY 078101 Overcoming Decomposition with Order-Reversed Quenching Obtained by Flash Melting SI Ping-Zhan, XIAO Xiao-Fei, FENG He, YU Sen-Jiang, GE Hong-Liang 078501 A Low Specific on-Resistance SOI Trench MOSFET with a Non-Depleted Embedded p-Island FAN Jie, ZHANG Bo, LUO Xiao-Rong, LI Zhao-Ji 078502 High-Efficiency InGaN/GaN Nanorod Arrays by Temperature Dependent Photoluminescence WANG Wen-Jie, CHEN Peng, YU Zhi-Guo, LIU Bin, XIE Zi-Li, XIU Xiang-Qian, WU Zhen-Long, XU Feng, XU Zhou, HUA Xue-Mei, ZHAO Hong, HAN Ping, SHI Yi, ZHANG Rong, ZHENG You-Dou

078503 A Distributed Phase Shifter Using Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 Thin Films LI Ru-Guan, JIANG Shu-Wen, GAO Li-Bin, LI Yan-Rong 078801 Optimization of Metal Coverage on the Emitter in n-Type Interdigitated Back Contact Solar Cells Using a PC2D Simulation ZHANG Wei, CHEN Chen, JIA Rui, Janssen G. J. M., ZHANG Dai-Sheng, XING Zhao, Bronsveld P. C. P., Weeber A. W., JIN Zhi, LIU Xin-Yu

COMMENTS AND REPLIES 079901 Comment on “Improvement of Controlled Bidirectional Quantum Direct Communication Using a GHZ State” [Chin. Phys. Lett. 30 (2013) 040305] LIU Zhi-Hao, CHEN Han-Wu 079902 Reply to the Comment on “Improvement of Controlled Bidirectional Quantum Direct Communication Using a GHZ State” [Chin. Phys. Lett. 30 (2013) 040305] YE Tian-Yu, JIANG Li-Zhen 079903 Comment on “Cryptanalysis and Improvement of a Quantum Network System of QSS-QDC Using χ-Type Entangled States” [Chin. Phys. Lett. 29 (2012) 110305] LIU Zhi-Hao, CHEN Han-Wu 079904 Reply to the Comment on “Cryptanalysis and Improvement of a Quantum Network System of QSS-QDC Using χ-Type Entangled States” [Chin. Phys. Lett. 29 (2012) 110305] GAO Gan, FANG Ming, CHENG Mu-Tian