Ab initio determination of polarizabilities and van der Waals coefficients of Li atoms using the relativistic coupled-cluster method

We report on a technique to determine the van der Waals coefficients of lithium (Li) atoms based on relativistic coupled-cluster theory. These quantities are determined using the imaginary parts of the scalar dipole and quadrupole polarizabilities, which are evaluated using an approach that we have proposed earlier [B. K. Sahoo, Chem. Phys. Lett. 448, 144 (2007)]. Our procedure is fully ab initio, and avoids the sum-over-the-states approach. We present the dipole and quadrupole polarizabilities of many of the low-lying excited states of Li. Also, the off-diagonal dipole and quadrupole polarizabilites between some of the low-lying states of Li have been calculated.

Figure 1

Extra correlation diagrams which appear in the calculation of the polarizabilities using our novel approach. These diagrams do not appear when the CC wave functions are used in the sum-over-the-states method.

Figure 2

The correlation diagram that causes a large discrepancy between the calculated and the experimental results of the tensor polarizability of the ${{}^{2}P}_{3/2}$ state.

Figure 3

The imaginary parts of the dipole (i) and quadrupole (ii) polarizabilities of the ground state of Li as a function of the angular frequency $\omega$.

Figure 4

The difference between the DF and CCSD(t) results for the imaginary parts of the dipole (i) and quadrupole, (ii) polarizabilities of the ground state of Li as a function of the angular frequency $\omega$.