Showing papers by "Christof Hättig published in 1996"

Intermolecular interaction energies by topologically partitioned electric properties. 1. Electrostatic and induction energies in one-centre and multicentre multipole expansions

Abstract: Certain difficulties with the usual one-center multipole expansion of long-range intermol. interaction energies can be circumvented by multicenter multipole expansions using several expansion sites in each mol., such as, e.g., the nuclear positions. Based on the topol. partitioning of the mol. vol. provided by Bader's 'atoms in mols.' theory, a method has been developed for calcg. the required at. multipole moments and polarizabilities. The performance of these topol. partitioned elec. properties is examd. for the calcn. of multipole expanded first-order electrostatic and second-order induction energies by comparing their convergence behavior with that of the corresponding one-center expansions. The homomol. dimers of the water, carbon monoxide, cyanogen, and urea mols. serve as examples. The results show that distributed elec. properties calcd. within the topol. partitioning scheme indeed solve the 'shape' convergence problem, which arises in the calcn. of interaction energies of large nonspherical mols. via multipole expansions.

Transferability of topologically partitioned polarizabilities: the case of n-alkanes

Abstract: Distributed polarizabilities of a series of n-alkanes C n H2n+2 (n = 2-7) in various conformations have been determined using Bader's topological theory of atoms in molecules. Using an appropriate localization scheme, a simple distributed model is constructed, where the methyl and methylene groups are characterized by their dipole polarizability tensors in local frames, and all charge flow polarizabilities between them are retained. A set of average polarizability parameters is proposed that takes into account the local environment of the methyl and methylene groups, and that not only reproduces the polarizability tensor for any member of the n-alkane series in an arbitrary conformation, but also is suitable for the calculation of induction energies.

TDMP2 calculation of dynamic multipole polarizabilities and dispersion coefficients of the triplebonded molecules CO, N2, CN−, and NO+

Abstract: In order to test the performance of the recently developed time‐dependent second‐order Mo/ller–Plesset perturbation theory (TDMP2) for anisotropic frequency‐dependent multipole polarizabilities, we have studied the isoelectronic series CO, N2, CN−, and NO+. The polarizabilities of these triple‐bonded diatomics are an interesting test for the TDMP2 method, because it is known that Mo/ller–Plesset perturbation theory has its difficulties describing multiple bonds. We selected these molecules as test systems because, especially for N2 and CO, accurate experimental and other ab initio data are available to compare with and their dynamical polarizabilities are needed for dispersion coefficients of van der Waals complexes, which are presently under intensive investigation. To get reliable results near the TDMP2 basis set limit we used large one‐particle basis sets, optimized for polarizability calculations at the coupled Hartree–Fock level. The results show that the TDMP2 method is capable to improve for the is...

Topologically partitioned dynamic polarizabilities using the theory of atoms in molecules

Abstract: Frequency-dependent distributed polarizabilities have been determined from time-dependent Hartree–Fock calculations, using the partitioning of the molecular space suggested by Bader's topological t...