Nonadditivity and anisotropy of the polarizability of clusters: Relativistic finite-field calculations for the Xe dimer

We present all-electron relativistic studies of the polarizability properties of the Xe dimer. The studies rely on finite-field calculations of the dimer energies obtained by ab initio methods including electron correlations. An extended set of basis functions is designed in order to ensure a high accuracy of the calculations. Particular attention is paid to the analysis of the nonadditivity and anisotropy of the polarizability of the dimer. It is found that the polarizability of the dimer relative to that of the atoms can be accurately described analytically, at least for internuclear distances around and larger than the equilibrium distance of the dimer.

Figure 1

Sum of the polarizabilities of the independent atoms separated by the distance $R$. The polarizability of each atom is obtained in the presence of the ghost basis set attributed to the location of the other atom. Dots are the results of the finite-field polarizability calculations for the discrete values of $R$. Solid lines connect the polarizability values for the electric field directed along the interatomic axis, and dashed lines connect the polarizability values for the perpendicular field direction.

Figure 2

Dimer polarizabilities as functions of the internuclear distance. The top and bottom panels show the longitudinal and transverse polarizabilities, respectively. Dots represent the results computed for the discrete values of the distance and are connected by the smooth solid lines for visualization of the curves. Different curves correspond to the different theoretical finite-field approaches labeled by SCF, MBPT2, CCSD, and CCSD(T) (MBPT2 and CCSD results are indistinguishable in the figure).

Figure 3

Relative polarizabilities versus internuclear distance. Triangles, squares, and dots (connected by the smooth solid lines) show the SCF, MBPT2, and CCSD(T) results. Dashed lines are the polarizability curves according to the DID model. The inset shows the curves for the domain of small distances where the finite-field results deviate from those of the DID model and where minor discrepancies appear in the results obtained at the SCF, MBPT2, and CCSD(T) levels.

Figure 4

Dimer interaction energy.