A BSSE-corrected CASSCF/NEVPT2 procedure. An application to weakly bonded OH..pi heterodimer complexes. Fanis G. Kalatzis, Ioannis N Demetropoulos To cite this version: Fanis G. Kalatzis, Ioannis N Demetropoulos. A BSSE-corrected CASSCF/NEVPT2 procedure. An application to weakly bonded OH..pi heterodimer complexes.. Molecular Physics, Taylor & Francis, 2008, 105 (17-18), pp.2335-2343. 10.1080/00268970701604689. hal-00513135 HAL Id: hal-00513135 https://hal.archives-ouvertes.fr/hal-00513135 Submitted on 1 Sep 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Molecular Physics For Peer Review Only A BSSE-corrected CASSCF/NEVPT2 procedure. An application to weakly bonded OH..pi heterodimer complexes. Journal: Molecular Physics Manuscript ID: TMPH-2007-0210 Manuscript Type: Full Paper Date Submitted by the 06-Jul-2007 Author: Complete List of Authors: Kalatzis, Fanis; University of Ioannina, Chemistry Demetropoulos, Ioannis; University of Ioannina, Chemistry CASSCF, NEVPT2, BSSE, Weakly bonded complexes, OH..ğ Keywords: intermolecular interactions URL: http://mc.manuscriptcentral.com/tandf/tmph Page 1 of 45 Molecular Physics 1 2 3 4 5 6 7 8 9 10 A BSSE-corrected CASSCF/NEVPT2 procedure. An application to 11 12 weakly bonded OH..π heterodimer complexes. 13 14 15 16 For Peer Review Only 17 [a] [a,b] 18 Fanis G. Kalatzis and Ioannis N. Demetropoulos 19 20 [a]Department of Chemistry, University of Ioannina, GR-45110, Ioannina, Greece. 21 22 [b]Department of Information and Telecommunications Engineering, Section of Applied 23 24 25 Informatics, University of West Macedonia, Park Agiou Dimitriou, Kozani, GR 50100, 26 27 Greece. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 [b]Corresponding Author: 46 47 48 Phone Number: +302651098449 49 50 Fax Number: +302651098798 51 52 53 54 55 e-mail: Fanis G. Kalatzis ([email protected]), Ioannis N. Demetropoulos ([email protected]) 56 57 58 59 60 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 2 of 45 1 2 3 4 5 6 Abstract 7 8 9 In this work a stable NEVPT2-based computational procedure was developed, capable to 10 11 study weakly bonded OH..π heterodimer complexes. The procedure was applied to the 12 13 evaluation of the weak OH..π intermolecular interaction energy of the ethene-water C2H4-H2O 14 15 complex, as a model case. The counterpoise method of Boys and Bernardi was used with the 16 For Peer Review Only 17 18 strongly contracted (SC) and partially contracted (PC) variants of the NEVPT2 method and 19 20 the energetic results were benchmarked against CCSD(T) calculations. In particular, for the 21 22 first time a computational methodology is proposed for the appropriate specification of the 23 24 25 active space in order to study weakly bonded OH..π heterodimer complexes, using the super- 26 27 molecular approach. The treatment of weakly bonded OH..π and van der Waals complexes 28 29 using CASSCF wavefunctions with second order perturbation theory seems to render 30 31 32 trustable and accurate results. Also, the present methodology suggests an efficient way for the 33 34 specification of the “ghost” basis functions in the multiconfigurational heterodimer case. The 35 36 Basis Set Superposition Error (BSSE) was eliminated in both CASSCF(2,2) and 37 38 39 CASSCF(10,7) selected case studies of the C2H4-H2O dimer. The behavior of BSSE lowering 40 41 as the basis set increases was verified. The computational procedure which was developed in 42 43 this paper can be easily adapted to the multiconfigurational NEVPT2 treatment of a large 44 45 variety of weakly bonded heterodimers. Finally, the procedure was successfully tested in the 46 47 48 benzene-water heterodimer. 49 50 51 Keywords: CASSCF, NEVPT2, BSSE, weakly bonded complexes, OH..π intermolecular 52 53 interactions. 54 55 56 57 58 59 60 1 URL: http://mc.manuscriptcentral.com/tandf/tmph Page 3 of 45 Molecular Physics 1 2 3 4 5 6 Introduction 7 8 9 An accurate exploitation of the weakly bonded intermolecular potential energy surface may 10 11 benefit by the inclusion of electron correlation through multiconfigurational wavefunctions. 12 13 Recalling the classification of Jeffrey[1], weak-bound hydrogen bonded complexes are 14 15 associated with energies below 4 Kcal/mol and the quantitative determination of these relative 16 For Peer Review Only 17 [2] 18 weak forces between molecules is experimentally and theoretically demanding. The 19 20 simplest case of a OH..π type intermolecular interaction is the ethene-water complex, which 21 22 can be sufficiently deployed to develop new computational procedures concerning the study 23 24 [3] 25 of weakly bonded heterodimer complexes. Previous experimental results using the 26 27 molecular beam electric resonance technique[3] and a thorough matrix isolation study[4] 28 29 exhibited a weak OH..π hydrogen bond perpendicular to the ethene plane. In both cases the 30 31 32 hydrogen atom is directed toward the center of the π-orbital of ethene. 33 34 The extension of the single reference self-consistent field wavefunction to the 35 36 multiconfigurational self-consistent field (MCSCF) wavefunction has been proved an 37 38 39 accurate estimate of the non-dynamical electron correlation. A well-applied implementation 40 [5] 41 of the MCSCF method is known as the complete active space (CASSCF) or full-optimized 42 43 reaction space (FORS)[6] method. The non-dynamical correlation energy may be defined as 44 45 the difference between full configuration interaction (CI) within the space of all valence 46 47 48 orbitals and a single determinant of molecular orbitals (Hartree–Fock theory). The exact 49 50 calculation of nondynamical correlation energy, involves computational complexity that 51 52 grows exponentially with molecular size. 53 54 55 An improved description of the multiconfigurational intermolecular potential energy surface 56 57 can be enhanced by the inclusion of dynamical electron correlation. The largest contribution 58 59 60 2 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 4 of 45 1 2 3 4 5 6 of the dynamical electron correlation is recovered by the perturbation theory approach which 7 8 9 essentially preserves the size-consistency of the reference multiconfigurational 10 [7] 11 wavefunction. To the best of our knowledge, several methods have been developed in order 12 13 to extend single-reference perturbation theory to multireference perturbation theory, based on 14 15 a zeroth-order MCSCF wavefunction. The most popular variant is the CASPT2 (second-order 16 For Peer Review Only 17 [8,9] 18 perturbation theory based on a CASSCF reference wavefunction) method. 19 20 Recently, a new variant of multireference perturbation theory, based on a CASSCF zeroth- 21 22 order wave function, called n-electron valence state perturbation theory NEVPT2, has been 23 24 [10,11,12] 25 proposed. The main advantages of this formulation are the strict separability (size- 26 27 consistency) and the absence of intruder states[13], at least in principle. Three different variants 28 29 of this method have been formulated, the strongly contracted (SC), partially contracted (PC), 30 31 32 and uncontracted variants. The SC and PC variants to second order NEVPT2, utilizing 33 [14] [15] 34 Dyall’s Hamiltonian , have been implemented in the Dalton 2.0 program. The two 35 36 variants differ by the number of perturber functions employed in the perturbation summation. 37 38 39 The PC–NEVPT2 uses a richer function space and is in general more accurate than the SC– 40 41 NEVPT2. The results of SC–NEVPT2 and PC–NEVPT2 are anyway usually very close to 42 43 one another. 44 45 In this work, a stable NEVPT2-based computational procedure was developed, capable to 46 47 48 allow the efficient study of weakly bonded OH..π heterodimer complexes. Besides, this 49 50 procedure provides a methodology for the identification of the appropriate active space 51 52 required to evaluate the intermolecular interaction energy of OH..π heterodimers. Considering 53 54 55 the C2H4-H2O heterodimer as a model case, the procedure was applied to the investigation of 56 57 its intermolecular interaction energy using the SC and PC variants of the NEVPT2 method. 58 59 60 3 URL: http://mc.manuscriptcentral.com/tandf/tmph Page 5 of 45 Molecular Physics 1 2 3 4 5 6 Preliminary CI calculations using small basis sets were performed to determine the active 7 8 9 molecular orbitals (MOs) and visualization tools were involved. Actually two different active 10 11 spaces were used in this study with a variety of basis sets. The stable convergence of the 12 13 NEVPT2 method was achieved in all cases. The size-consistency of CASSCF and NEVPT2 14 15 methods efficiently allows such multireference calculations. 16 For Peer Review Only 17 18 Another feature of the developed procedure is related with the elimination of the basis set 19 20 superposition error (BSSE) at the NEVPT2 theory, using the super-molecular approach. The 21 22 most common procedure to remove the BSSE is the counterpoise (CP) method of Boys and 23 24 [16] 25 Bernardi. The CP method calculates each of the monomers’ energy on the basis set of the 26 27 other, using “ghost” atoms.