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Power for Quantum Tools Chemists ADF The universal density functional package for chemists! The ADF density functional package • Properties and environments for any molecule • Excels in transition and heavy metal compounds • Fast, robust, and accurate • Expert support and active user community • Uses Slater functions, beats Gaussians! 1 I Introduction Ia ADF The Amsterdam Density Functional package (ADF) is software for first-principles electronic structure calculations (quantum chemistry). ADF is used both by academic and by industrial researchers worldwide, in such diverse fields as pharmacochemistry and materials science. It is particularly popular in the research areas of homogeneous and heterogeneous catalysis, inorganic chemistry, heavy-element chemistry, biochemistry, and various types of spectroscopy. The package consists of the molecular ADF program, the periodic structure program BAND, and a graphical user interface (GUI) for ADF. Several smaller utility and property programs, as well as free third-party utilities, are available. ADF is based on Density Functional Theory (DFT), which has dominated quantum chemistry applications since the early 1990’s. DFT gives superior accuracy to Hartree-Fock theory and semi-empirical approaches. In contrast to conventional ab initio methods (MP2, CI, CC), it enables accurate treatment of transition metal compounds with hundreds of atoms (thousands with QM/MM). Ib Academic ADF development groups Historically, ADF has been developed mainly at the well-known theoretical chemistry groups in Amsterdam (Prof. Baerends and coworkers) and Calgary (Prof. Ziegler and coworkers). Nowadays, many academic developers across the US, Canada, and Europe are contributing further developments to ADF and BAND. 1c Scientific Computing & Modelling NV (SCM) Scientific Computing & Modelling NV (SCM) is a spin-off company of the Baerends group, established in 1995. Its primary mission is to assist in further development of ADF, and to support the ADF user community. The SCM staff consists of scientists with Ph.D. degrees in theoretical chemistry and with many years of experience in ADF development and applications. 1d Community The ADF users and developers form an active community. Topics of mutual interest are discussed on the ADF mailing list. A fully searchable archive of the mailing list is accessible from the SCM website. The academic developers are in close contact with each other and with SCM, thus ensuring rapid further development of ADF. 1 II Functionality The ADF package can be applied to isolated molecules, polymers, slabs, solids, molecules in solvents, and molecules in protein environments. It can treat all elements of the periodic table, and contains state-of-the-art relativistic methods (ZORA [1] and spin-orbit coupling) to treat heavy nuclei. ADF is especially suited for transition metal compounds. It is efficient due to a combination of linear scaling and parallelization techniques, and contains many standard methods for studying potential energy surfaces, as well as a wide range of molecular properties. Chemically relevant analysis methods are available (including bond energy decomposition, fragment orbitals, and charge decomposition). The QM/MM implementation enables the treatment of protein environments with many thousands of atoms. ADF includes the very latest meta-GGA and hybrid exchange-correlation functionals, as well as a full range of standard functionals (including B3LYP). IIa Geometry optimizations, transition states, reaction paths, and infrared frequencies ADF enables geometry optimizations in Cartesian and internal coordinates. An initial Hessian estimate speeds up the optimizations. Various constraints (including initially unsatisfied and combined) can be imposed. Transition state searches, intrinsic reaction coordinates, and linear transit calculations are available to further analyze the energy path from reactants, via the transition state, to the final products. A fast, parallel analytic second derivatives implementation yields IR frequencies and Hessians. These Hessians are helpful in finding and characterizing the transition states. 2 3 IIb Molecular properties An important strength of ADF is the variety of accessible molecular properties available and the accuracy with which they can be obtained. The time-dependent DFT implementation yields UV/Vis spectra (singlet and triplet excitation energies, as well as oscillator strengths, fig. 1), frequency-dependent (hyper-)polarizabilities (nonlinear optics), Raman intensities, and van der Waals dispersion coefficients. Rotatory strengths and optical rotatory dispersion (optical properties of chiral molecules) as well as frequency-dependent dielectric functions for periodic structures are available. NMR chemical shifts and spin-spin couplings, ESR (EPR) g-tensors, magnetic and electric hyperfine tensors, and nuclear quadrupole coupling constants can all be calculated, as well as more standard properties like IR frequencies and intensities, and multipole moments. Relativistic effects (ZORA and spin-orbit coupling) can be included for most properties. The implementation of most of these properties, including optical and NMR properties, fully exploits the speed-ups of parallel computers. B Q M Fig. 1 Gas phase optical absorption spectrum "L" N of Ni-octaethylporphyrin. Spectra of Optical density (metal) porphyrins and related compounds 200 300 400 500 600 700 800 can be understood in detail through ADF Wavelength (nm) calculations [2]. IIc Modeling solvents, proteins, and other environments The conductor-like screening model (COSMO) is available for molecules in a solvent. The QM/MM implementation enables treatment of active sites in protein environments with many thousands of atoms. Homogeneous electric fields and point charges can be specified. 2 3 IId Graphical User Interface A full Graphical User Interface for ADF (ADF- GUI) is being developed and released module by module. The input builder ADFinput enables all users to set up very complicated calculations with a few mouse clicks (fig. 2). Fig. 2 The ADFinput module of the ADF-GUI allows users to build or import a molecule, and select the appropriate options rapidly. ADFview provides graphical representations of many parts of the output, such as the computed Kohn-Sham orbitals, deformation densities and electrostatic potentials (fig. 3), the Electron Localisation Function (ELF), and many more. ADFspectra (fig. 4) visualizes spectra (such as IR, optical, and DOS), and ADFmovie displays the nuclear displacements during a geometry optimization or molecular vibration. High priority is given to further enhancements of the ADF- GUI. Fig. 3 The values of the electrostatic potential of a porphyrin sandwich molecule are shown in color on an isodensity surface. Fig. 4 The ADFspectra module can display various types of molecular spectra calculated by ADF. 4 5 IIe Polymers, slabs, and solids with BAND BAND is a periodic structure program for the study of bulk crystals, polymers, and surfaces. It uses numerical and Slater atomic orbitals and avoids pseudo-potential approximations. BAND is often used in heterogeneous catalysis studies. It provides densities-of-states (total, partial, population) analyses, and the Potential Energy Surface (PES) of, for instance, a chemisorption system or a chemical reaction at a metal surface (fig. 5). Fig. 5 PES for H2 on three-layer platinum slab for study on dissociative adsorption and direct absorption (work by O.M. Løvvik and R. Olsen). BAND offers a variety of density functionals, and the choice between spin-restricted and spin-unrestricted calculations. It provides an analysis of the ‘bonding’ (cohesive) energy in conceptually useful components, Mulliken-type population analyses, and the charge density Fourier analysis (form factors). A fragment analysis feature is available for decomposition of Density-of-States data in terms of the molecular orbitals of (molecular) fragments. BAND uses the same relativistic methods as ADF and is well suited to treat heavy nuclei. A time-dependent DFT implementation enables the accurate calculation of frequency-dependent dielectric functions 32 (fig. 6). Further work on magnetic and 24 electric properties of extended systems 16 is ongoing. 8 0 1.5 3 4.5 6 Fig. 6 Comparison of theoretical and experimental Non relativistic (NR) Scalar Relativistic (SR) results for the imaginary part of the Experiment dielectric function of solid InSb [3]. 4 5 III Analysis ADF contains several unique analysis options, offering the possibility of gaining detailed understanding of the chemical problem at hand. These methods stress the underlying philosophy that the Kohn-Sham orbitals in DFT can be used for a ‘quantitative MO theory’ [4]. IIIa Molecule built from fragments ADF and BAND analyze their results in terms of user-specified subsystems from which the total system is built. The program tells you how the ‘fragment orbitals’ (FO’s) of the chemically meaningful sub-units mix with FO’s on other fragments to combine to the final molecular orbitals (fig. 7). Fig. 7 Analysis of the electronic structure of porphyrin rings in terms of 4 pyrrolic fragments, made possible by the fragments option in ADF. 6 7 IIIb Bond energy analysis ADF calculates various chemically meaningful terms that add up to the bond energy, with an adaptation [5, 4] of Morokuma’s bond energy decomposition to the Kohn-Sham MO method. The individual terms are chemically intuitive quantities such as electrostatic energy, steric repulsion, Pauli repulsion, and
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