Enhanced linear and nonlinear polarizabilities for the Li4 cluster.: How satisfactory is the agreement between theory and experiment for the static dipole polarizability?

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)over bar> = 387.01 and Delta alpha = 354.60 e(2)a(0)(2)E(h)(-1). The mean hyperpolarizability is <(gamma)over bar> = 2394 x 10(3) e(4)a(0)(4)E(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(2)a(0)(2)E(h)(-1)) of this important quantity [Benichou et al. Phys. Rev. A 1999, 59, R1].