Ab initio structures and polarizabilities of sodium clusters

We present quantitative ab initio calculations for Na cluster structures an d polarizabilities, for all cluster sizes up to 20 atoms. Our calculations are performed by combining an ab initio core-corrected pseudopotential and a gradient-corrected density functional within a real space approach. We fi nd the cluster bonding to be very floppy and catalog a host of low-energy q uasi-degenerate isomers for all second-decade clusters. The existence of th ese isomers results in a band of polarizability values for each cluster siz e even at zero temperature. This eliminates any finer structure in the pola rizability curve. We further show that the experimental polarizability valu es are consistently underestimated by calculations at zero temperature. By computing the effects of structure expansion and distortion due to a finite temperature we arrive at a quantitative agreement between theory and exper iment. (C) 2001 American Institute of Physics.