G. te Velde

Chemistry with ADF

We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order‐N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency‐dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF‐typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation‐strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time‐dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena.

Numerical integration for polyatomic systems

Abstract A numerical integration package is presented for three-dimensional integrals occurring in electronic structure calculations, applicable to all polyatomic systems with periodicity in 0 (molecules), 1 (chains), 2 (slabs), or 3 dimensions (crystals). The scheme is cellular in nature, based on Gaussian product formulas and it makes use of the geometrical symmetry. Convergence of accuracy with the number of points is rapid and use of the program has been made easy.

Slab versus cluster approach for chemisorption studies. CO on Cu (100)

Abstract Local density functional (LDF) slab calculations exhibit good convergence for the chemisorption energy with the number of substrate layers and with the adsorbate-adsorbate distance, in contrast with the poor convergence with cluster size and shape commonly observed in cluster calculations. The major discrepancy of cluster calculations for Cu/CO with experiment, i.e. strong preference for the hollow site, does not recur in the slab calculations, although the hollow site is still slightly preferred. The local density approximation yields an overbinding of ≈ 75 kJ/mol, at top sites in line with the LDA overbinding for metalligand bonds and for bond energies in general.

The effect of density-gradient corrections for a molecule-surface potential energy surface. Slab calculations on Cu(100)c(2x2)-CO

Abstract We have performed slab calculations on the periodic adsorption, with a coverage θ = 0.5, of CO on the Cu(100) surface. Using nonlocal corrections to the local density approximation (LDA), the calculated chemisorption energy is 0.7 eV, and the top site slightly preferred over the hollow site. These results are in substantially better agreement with the experiment than the LDA results. The structure and vibrational frequencies are not much influenced.

All-electron Dirac-Fock-Slater SCF calculations for electronic and geometric structures of the Hg₂ and Hg₃ molecules.

The electronic and geometrical structure of neutral and cationic Hg2 and Hg3 molecules are calculated using the all-electron Dirac-Fock-Slater SCF method, with relativistic numerical atomic basis functions. An improved calculation of the direct Coulomb potential has been taken into account in order to get a numerically accurate potential energy surface. The binding, ionization and excitation energies have been compared with experimental results as well as other theoretical results.

Spectroscopy of even Sn nuclei and generalized-seniority breaking

Abstract Properties of even Sn nuclei are described in a broken-pair or generalized-seniority ( ν g ) scheme. Special attention is paid to the degree of ν g mixing in various types of low-lying states. A finite-range interaction as well as a surface-delta interaction (SDI) are employed and single-particle energies are deduced from spectra of odd Sn isotopes. It appears that up to 3 MeV no experimental indications for states with ν g > 4 exist. The only low-lying states which are not included in the model are the members of the well-known two-proton-hole band. With the SDI the ν g mixing is in general a factor two less than with the finite-range force. For the latter an improvement of the description of energy spectra as well as electromagnetic decay is obtained due to about 20% ν g = 4 admixtures in predominantly ν g = 2 states. Only ground states, 2 1 + and 3 1 − states have less than 10% of ν g = 4 admixtures. We argue that the main origin of ν g mixing is a particle-phonon coupling mechanism. A strong fragmentation of two-phonon 0 + , 2 + , 4 + states by ν g mixing emerges from the calculations. For the 0 + states the total two-phonon E2 transition strength is much less than predicted by phenomenological phonon or boson models. Excitation strengths for unnatural-parity states are reduced by 30–40% by ν g mixing. For natural-parity states this reduction is less; for 2 1 + and 3 1 − enhancements by ground-state correlations overcompensate the reduction by fragmentation.

Analysis of the polarizability and optical properties of

The interaction between electromagnetic radiation and the molecule has been analysed by an evaluation of the low-energy part of the linear response spectrum of buckminsterfullerene, . Single-particle wavefunctions, determined from local-density ground-state calculations, were used for evaluation of dipole matrix elements which, combined in a sum-over-states approach, yielded wavelength-dependent free-response microscopic linear polarizabilities. Screening of the external electromagnetic field through the induced charge distribution was determined by applying external static electric fields in separate self-consistent field calculations and by evaluation of the induced dipole moment. The polarizability calculated in the static limit was used to determine an effective screening parameter for evaluation of the dynamic response. The inclusion of screening was found to give an optical spectrum in rather good agreement with the corresponding experimentally determined spectrum of , in the gas phase or solution, by absorption measurements, EELS or photoionization techniques. Furthermore, by the use of Lorentz local field factors, we find a similar agreement for the dielectric function determined from ellipsometry and EELS measurements. In the above cases, the shapes of the spectra are essentially reproduced except for a uniform shift of about 0.5 eV to the low-energy side in the region and about 4 eV in the opposite direction in the region above 10 eV.