Electronic structure and electric properties of the alkali metal dimers

Abstract

Dipole moments and dipole polarizabilities of a series of the alkali metal atom dimers involving Li, Na, K, and Rb are calculated at the level of different coupled cluster approximations as well as the complete active space self-consistent-field approach followed by the perturbation treatment of the dynamical correlation effects. All reported calculations have been carried out with recently developed polarized basis sets. The electron correlation effects on these electric properties are studied within the valence and valence plus next-to-valence shell approximations. Also the relativistic contribution is calculated by using the quasirelativistic scalar (mass–velocity+Darwin terms) approximation. A comparison of results of different methods indicates that the values calculated by the coupled clusters method in which one- and two-electron clusters are treated iteratively and the three-body terms perturbatively [as defined in the CCSD(T) method] are well saturated in terms of the electron correlation contribution to molecular electric properties of the dimers. The achieved agreement with available experimental data is for most molecules fairly good. The interpretation of the electric property data is based on the analysis of the valence and core-polarization contributions and the observed regularities are elucidated in terms of simple molecular orbital ideas. The dipole moments of the heteronuclear dimers follow the pattern predicted by electronegativities of the two atoms. The perpendicular component of the electric dipole polarizability has been found to mostly reflect its atomlike origin, while the parallel one is intimately related to the electronic structure of the week bonding in the dimers. The relativistic effect becomes of certain importance only for the rubidium compounds. The results of our calculations are compared with ab initio and empirical pseudopotential data and with more recent calculations using the density functional theory methods. Our results indicate that the density functional methods lead to fairly reliable polarizability data, though they depend on the choice of the exchange and exchange-correlation potentials.

Ab Initio Studies of Properties of Small Potassium Clusters

“…The static polarizability plays an important role in the charctarization of the clusters and it is one of the property which has been extensively We begin our discussion on the results for polarizabilities by first testing the accuracies of SAOP and MP2 results for dimer and tetramer against the corresponding data obtained with a large basis set coupled cluster theory with single and double excitations and perturbative triple excitation (CCSD(T)) calculations [33]. In Table IV we present the results for polarizabilities of K 2 and K 4 obtained with three different methods along with the other theoretical [31,56] and experimental [18,57] results for the dimer which are already available in literature. From Table IV, we notice that the results for the dimer obtained by CCSD(T) approach vary from 486 to 510 a.u.…”

Variational calculation of vibrational linear and nonlinear optical properties

“…58 These basis sets have given satisfactory polarizabilities for a large number of molecules. [59][60][61][62][63] The field-dependent geometry optimizations were done by our own program which rigorously enforces the Eckart conditions. 64 There is an uncertainty in the calculated P c that arises because of the numerical differentiations involved.…”

Electric dipole polarizabilities and C6 dipole-dipole dispersion coefficients for sodium clusters and C60

“…At the microscopic level, the interaction energy and the C 6 dispersion coefficients are directly related to the electric dipole polarizability according to the Casimir-Polder relation. 2 The original measurements by Knight et al 3 of the polarizability of sodium clusters containing up to 40 atoms have spurred a large number of theoretical calculations [4][5][6][7][8][9] and experiments [10][11][12] devoted to the ground state electronic structure and optical properties of these systems. Sodium clusters attract interest not only because they are fundamental metal clusters with available experimental data but also due to their physical and chemical properties.…”