Charge distribution in the nitrate ion

The difference electron density in the nitrate ion is studied by comparison of some Hartree-Fock-Slater calculations. It is shown that good qualitative agreement with experiment is obtained

Charge density study with the Maximum Entropy Method on model data of silicon. A search for non-nuclear attractors

1990 Sakata and Sato applied the maximum entropy method (MEM) to a set of structure factors measured earlier by Saka and Kato with the Pendellösung method. They found the presence of non-nuclear attractors, i.e., maxima in the density between two bonded atoms. We applied the MEM to a limited set of Fourier data calculated from a known electron density distribution (EDD) of silicon. The EDD of silicon was calculated with the program ADF-BAND. This program performs electronic structure calculations, including periodicity, based on the density functional theory of Hohenberg and Kohn. No non-nuclear attractor between two bonded silicon atoms was observed in this density. Structure factors were calculated from this density and the same set of structure factors that was measured by Saka and Kato was used in the MEM analysis. The EDD obtained with the MEM shows the same non-nuclear attractors that were later obtained by Sakata and Sato. This means that the non-nuclear attractors in silicon are really an artefact of the MEM

Density Functional Study of Ground and Excited States of MnC2(CO)C10

The precise nature of the excited states of Mn2(CO)lo leading to the well-known photochemistry-both Mn-Mn and Mn-CO bond breaking upon low-energy excitation-is still unclear. In order to identify possibly dissociative excited states (either Mn-Mn, Mn-CO,, or Mn-CO,,), the nature of the highest occupied Mn-3d orbitals is analyzed as well as the composition of the virtual orbitals. The following features are noted. (a) The low-energy excitations at 337-355 nm arise from B - CJ* and dn - u* excitations, while d - d excitations occur at much higher energy. (b) The Mn-Mn CJ bonding HOMO as well as the u* LUMO cannot simply be classified as arising from the 3d,2 components of eg parentage in the local octahedrons around Mn, they have little 3d,2 - 3d,2 (anti)bonding character but significant contributions come from M n - 4 ~ a~n d CO-2ne,, orbitals. Mn-Mn B antibonding is only strong in the B* orbital due to these contributions. (c) Due to the strong involvement of Mn-4p2, th 3d,2 orbital not only occurs in the B and u* orbitals but also in a higher set of virtuals, denoted d,d*, -1.5 eV above the u* orbital. Antibonding with axial CO’s is strong in these higher virtuals but absent or weak in the B and CJ* orbitals. CJ antibonding with equatorial CO’s is strong in the 3d2+ orbital of eg parentage, that is located very high in the virtual spectrum, -2 eV above the u* orbital. Mn-Mn dissociation will occur only from the B - B* excitation; CO loss will probably occur from the high-lying d - d excited states (excitations into d,d* and 3d2-,2). The observed photochemistry at low energy will have to be explained from curve crossings between the low-energy excited states and the photoactive states

Erratum: “Calculating frequency-dependent hyperpolarizabilities using time-dependent density functional theory” [J. Chem. Phys. 109, 10644 (1998)]

An accurate determination of frequency-dependent molecular hyperpolarizabilities is at the same time of possible technological importance and theoretically challenging. For large molecules, Hartree–Fock theory was until recently the only available ab initio approach. However, correlation effects are usually very important for this property, which makes it desirable to have a computationally efficient approach in which those effects are (approximately) taken into account. We have recently shown that frequency-dependent hyperpolarizabilities can be efficiently obtained using time-dependent density functional theory. Here, we shall present the necessary theoretical framework and the details of our implementation in the Amsterdam Density Functional program. Special attention will be paid to the use of fit functions for the density and to numerical integration, which are typical of density functional codes. Numerical examples for He, CO, and para-nitroaniline are presented, as evidence for the correctness of the equations and the implementation.<br/

Improved density functional theory results for frequency-dependent polarizabilities, by the use of an exchange-correlation potential with correct asymptotic behavior.

The exchange‐correlation potentials vxc which are currently fashionable in density functional theory (DFT), such as those obtained from the local density approximation (LDA) or generalized gradient approximations (GGAs), all suffer from incorrect asymptotic behavior. In atomic calculations, this leads to substantial overestimations of both the static polarizability and the frequency dependence of this property. In the present paper, it is shown that the errors in atomic static dipole and quadrupole polarizabilities are reduced by almost an order of magnitude, if a recently proposed model potential with correct Coulombic long‐range behavior is used. The frequency dependence is improved similarly. The model potential also removes the overestimation in molecular polarizabilities, leading to slight improvements for average molecular polarizabilities and their frequency dependence. For the polarizability anisotropy we find that the model potential results do not improve over the LDA and GGA results. Our method for calculating frequency‐dependent molecular response properties within time‐dependent DFT, which we described in more detail elsewhere, is summarized

Accurate density functional calculations on frequency-dependent hyperpolarizabilities of small molecules

In this paper we present time-dependent density functional calculations on frequency-dependent first (β) and second (γ) hyperpolarizabilities for the set of small molecules,