Initio Way Research Articles

Theoretical investigation of hyperfine interactions and isotope shifts in gold

Use of relativistic many-body perturbation theory is made to calculate the hyperfine splitting of the ground 62S1/2 state in 197Au (I=3/2). The calculated splitting of 6068 MHz is in good agreement with the experimental value of 6099.320184(13) MHz determined by an atomic beam magnetic resonance technique. Electron charge densities at the nuclear surface corresponding to various configurations of 197Au are calculated in an ab initio way by numerically solving the relativistic Dirac-Fock equations incorporating the nuclear charge distribution. The electronic factor relevant to the volume isotope shift for the resonance transition 6s2S1/2-6p2P1/2 in gold is also calculated and compared with other available results.

Volume isotope shifts in low lying transitions of Au I

Electronic factors in the volume isotope shift have been calculated in anab initio way with the relativistic Dirac-Fock method for a number of different optical single/and two-photon transitions in Au I. The agreement with a semi-empirical method is within 10% for the resonance transition. For this one and a few other transitions the effect of core excitation has been analyzed with the Multi-configuration Dirac-Fock method as well, and it was found to reduce the electronic factor in the order of 5%.

Equilibrium structure and harmonic force field of the known PH3 and the unknown PH5

The equilibrium geometries and harmonic force fields of PH3 and PH5 are calculated in an ab initio way including electron correlation. The results for PH3 are in very good agreement with experimental values, whereas those for PH5 have to be regarded as predictions. We find for PH5 in its equilibrium D3h structure rax = 1.47 A, req = 1.42 A and the harmonic vibration frequencies in Table 7 given under the heading “CEPA”. The barrier for Berry inversion is 2 kcal/mol. The ab initio calculation of phosphoranes such as PH5 not only requires the inclusion of polarization functions (d on P and p on H) but is also very sensitive to the choice of these polarization functions. This problem is taken care of by a detailed comparison of various basis sets. It is confirmed that a (10/6) basis for P in “double zeta contraction” is better balanced than a (12/9) basis in “double zeta contraction” and that the total energy is not a good criterion for the quality of a basis.