Ab initio calculation on accurate analytic potential energy functions and harmonic frequencies of c3∑+g and B1∏u states of dimer 7Li2

摘要

The comparison between single-point energy scanning (SPES) and geometry optimization (OPT) in determining the equilibrium geometries of c3∑+g and B1∏u states of dimer 7Li2 is made at numerous basis sets by using a symmetryadapted-cluster configuration-interaction (SAC-CI) method in the Gaussian 03 program package. In this paper the difference of the equilibrium geometries obtained by SPES and by OPT is reported. The results obtained by SPES are found to be more reasonable than those obtained by OPT in full active space at the present SAC-CI level of theory. And the conclusion is attained that the cc-PVTZ is a most suitable basis set for these states. The calculated dissociation energies and equilibrium geometries are 0.8818 eV and 0.3090 nm for c3∑+g state, and 0.3668 eV and 0.2932 nm for B1∏u state respectively. The potential energy curves are calculated over a wide internuclear distance range from about 2.5a0 to 37a0 and have a least-squares fit into the Murrell-Sorbie function. According to the calculated analytic potential energy functions, the harmonic frequencies (ωe) and other spectroscopic data (ωeχe, Be and αe) are calculated. Comparison of the theoretical determinations at present work with the experiments and other theories clearly shows that the present work is the most complete effort and thus represents an improvement over previous theoretical results.