Enhanced Linear and Nonlinear Polarizabilities for the Li_4 Cluster. How Satisfactory Is the Agreement between Theory and Experiment for the Static Dipole Polarizability?

摘要

Highly accurate ab initio calculations with specially designed basis sets are reported for Li_4. The molecule emerges as a particularly soft system, with a very anisotropic dipole polarizability and a very large second dipole hyperpolarizability. An extensive investigation of basis set and electron correlation effects leads to values of #alpha#-bar = 387.01 and #DELTA##alpha# = 354.60 e~2a_0~2E_(h~(-1)). The mean hyperpolarizability is #gamma#-bar = 2394 * 10~3 e~4a_0~4E_(h~(-3)). The computational aspects of the present effort are discussed in view of the extension of quantumchemical studies to large lithium clusters. Our values for the mean dipole polarizability are systematically higher than the recently reported experimental static value (326.6 e~2a_0~2E_(h~(-1)) of this important quantity [Benichou et al. Phys. Rev. A 1999,59, R1].