No abstract

An extended geminal model has been applied to determine the interatomic potential for the X 1 ⌺ g ϩ state of Be 2 . By adopting a (23s, 10p, 8d, 6f, 3g, 2h) uncontracted Gaussian-type basis, the following spectroscopic parameters are obtained:

A standard Cholesky decomposition of the two-electron integral matrix leads to integral tables which have a huge number of very small elements. By neglecting these small elements, it is demonstrated that the recursive part of the Cholesky algorithm is no longer a bottleneck in the procedure. It is shown that a very efficient algorithm can be constructed when family type basis sets are adopted. For subsequent calculations, it is argued that two-electron integrals represented by Cholesky integral tables have the same potential for simplifications as density fitting. Compared to density fitting, a Cholesky decomposition of the two-electron matrix is not subjected to the problem of defining an auxiliary basis for obtaining a fixed accuracy in a calculation since the accuracy simply derives from the choice of a threshold for the decomposition procedure. A particularly robust algorithm for solving the restricted Hartree-Fock (RHF) equations can be speeded up if one has access to an ordered set of integral tables. In a test calculation on a linear chain of beryllium atoms, the advocated RHF algorithm nicely converged, but where the standard direct inversion in iterative space method converged very slowly to an excited state.

m An extended geminal model has been applied to determine the interatomic potential for the X'S: state Be,. By adopting a [lls,9p,6d,4f,2g] contracted Gaussian-type basis, the following potential minimum parameters are obtained: Re = 4.67 a.u. (4.63 a.u.1 and D, = 3.70 mH (3.82 0.05 mH), experimental values in parentheses. A calculation with a nuclei-centered [Ss, 7p, 4d, 2 f, 181 GTO basis plus two sets of bond-type function, each set comprising diffuse (2 s, 2 p , 2 d, 2f, 1 g) GTOs, yielded -3.79 mH as the value of the potential at R = 4.63 a.u. On the basis of an error analysis the best theoretical estimate of the binding energy is determined to be 3.83 k 0.08 mH. The calculated value for the fundamental vibrational frequency is vo

No abstract