Georg Jansen

Distributed polarizabilities using the topological theory of atoms in molecules

Distributed atom-atom multipolar polarizabilities have been calcd. at the coupled perturbed Hartree-Fock level, using Baders topol. theory to partition the mol. charge d. into at. domains. The proposed scheme applies without difficulty to mols. of arbitrary shape and symmetry and maintains a remarkable stability of the individual at. polarizability components with respect to basis set extension, exemplified by the mols. CO, H2O, NH3 and BF3.

Coupled-pair functional calculations on the Ar-CO and Ar2 van der Waals complexes

After an assessment of the equil. properties of Ar2 (De~75 cm-1, Re~7.32 Bohr) as detd. in supermol. coupled-pair functional calcns. in the limit of high angular momentum basis functions, the potential energy surface for interaction of an Ar atom with the CO mol. is presented. The calcd. potential energy surface has its abs. min. of De = 71 cm-1 at a T-shaped geometry. The barriers for rotation around the oxygen and carbon end of the complex have been found to be 13 and 21 cm-1, resp. The performance of averaged coupled-pair functional and averaged quadratic coupled-cluster techniques for calcn. of interaction energies of Ar2 and Ar-CO and for detn. of electrostatic moments and polarizabilities of the CO mol. is briefly discussed as well.

Ab initio interaction potentials between an Ar atom and the NH radical in the states X 3Σ−, a 1Δ and b 1Σ+

Abstract Using extended basis sets in complete active space self-consistent field and averaged coupled-pair functional calculations, the potential energy surfaces for the interaction of an Ar atom with the NH radical in its three lowest electronic states were determined. While the ground-state interaction energy surface was found to have its absolute minimum at a non-linear geometry of the Arue5f8NH complex, the other surfaces have their absolute minima at linear geometries with Ar next to H.

Relativistic all-electron configuration interaction calculations on the gold atom

Results of relativistic and non-relativistic SCF and CI calcns. are given for the gold atom, using the spin-free no-pair Hamiltonian in a basis set expansion. A new basis set for the gold atom is discussed and its results in relativistic and non-relativistic SCF calcns. are compared to those of numerical Dirac-Hartree-Fock and Hartree-Fock calcns., resp. Excitation energies, electron affinities, and ionization potentials were calcd. using a multi-ref. CI technique and are in reasonable agreement with expt. in the relativistic case.

The rovibrational spectrum of the ArCO complex calculated from a semiempirically extrapolated coupled pair functional potential energy surface

The rovibrational spectrum of the ArCO van der Waals complex has been calculated using a recently published ab initio potential energy surface determined by the coupled pair functional approach. Comparison with known experimental values for some of the transitions shows that the anisotropy of this surface comes out reasonably well, although its well depth of 72 cm−1 is too small. Based on a comparison of coupled pair functional interaction energies for Ne2, NeAr, and Ar2 with empirical potential energy curves an extrapolation scheme for the differential correlation energy is suggested. This semiempirical extrapolation scheme, with a slight modification to account for anisotropy, is also applied to the coupled pair functional interaction energies for ArCO, resulting in a surface which is characterized by a well depth of 109 cm−1 at a T‐shaped geometry and a barrier of 20 cm−1 for rotation of Ar around the oxygen end of CO and of 26 cm−1 for rotation around the carbon end. The rovibrational spectrum calcula...

Are direct reaction field methods appropriate for describing dispersion interactions

Abstract Direct reaction field (DRF) model Hamiltonians are used in various fields of quantum chemistry, for example in core polarization potentials and in solvent effect theories. The DRF method is usually claimed to be appropriate to describe the correlation (dispersion interaction) with other electron groups, which are not included explicitly in the calculation. It is shown that the C 6 coefficients resulting from the DRF theory are erroneous by a factor of 2 to 15 in a series of simple systems. The source of the error can be attributed to the unjustified assumption that the mean excitation energy of the explicitly treated subsystem is negligible with respect to the excitation energies of the other one. A more appropriate reaction field Hamiltonian is proposed which includes both “average” (nonlinear) and “direct” (linear) terms for polar solutes.

Theoretical investigation of the rovibrational fine-structure spectrum of ArNH in its electronic ground state

Abstract Based on an ab initio potential energy surface for the X 3 A″ ground state of the Arue5f8NH van der Waals complex its rovibrational fine-structure spectrum has been calculated. We find four Arue5f8NH stretching vibrational modes with the NH radical in a nearly unperturbed n =0 rotational state and one vibrational mode with NH in its first excited rotational level n =1. The results are discussed and interpreted by means of pseudodiatomic model calculations.

Solvent: A computer program for generalized self‐consistent reaction field calculations

The theoretical foundations and the implementation of a computer program for generalized self‐consistent field (GSCRF) calculations are described. The GSCRF model takes the microscopic structure of the environment of a solute explicitly into account; it models electrostatic interaction between the ab initio described solute and the classical solvent by distributed multipole moments and represents induction effects by electric polarizabilities of individual solvent molecules. High precision solute wave functions can be calculated at arbitrary level of theory in realistic solvent models. As examples the proton transfer of NH3...HCl in argon matrix and the electrostatic properties of a water molecule in liquid water are discussed.