A NEW TABLE-DIRECT CONFIGURATION-INTERACTION METHOD FOR THE EVALUATION OF HAMILTONIAN MATRIX-ELEMENTS IN A BASIS OF LINEAR-COMBINATIONS OF SPIN-ADAPTED FUNCTIONS
S. Krebs et Rj. Buenker, A NEW TABLE-DIRECT CONFIGURATION-INTERACTION METHOD FOR THE EVALUATION OF HAMILTONIAN MATRIX-ELEMENTS IN A BASIS OF LINEAR-COMBINATIONS OF SPIN-ADAPTED FUNCTIONS, The Journal of chemical physics, 103(13), 1995, pp. 5613-5629
A new table-direct CI (TDCI) scheme based on the table CI method for t
he direct computation of Hamiltonian matrix elements whose basis funct
ions are linear combinations of spin-adapted functions psi(alpha) is p
resented, in which the explicit calculation and storage of the Hamilto
nian matrix H in the basis {psi(alpha)} is avoided. Two algorithms are
provided for the matrix element evaluation; (i) within the iterative
Davidson diagonalization procedure of H and (ii) within the individual
ized configuration selection scheme of Buenker and Peyerimhoff, as inc
luded in the MRD-CI program of these authors. The new algorithm is emp
loyed to compute the equilibrium structural parameters of the lowest X
(2)A(1) and A B-2(2) states of NO2, solving secular equations of dime
nsion 190 000 spin-adapted functions (384 000 determinants, 32 000 con
figurations), as well as the T-e value for the corresponding transitio
n. (C) 1995 American Institute of Physics.