HD_AVG

How to average H diag energies over spin coupling sets. HD_EXACT uses the exact diagonal energies which results in expansion vectors which break spin symmetry. HD_KAVE averages the diagonal energies over a spin-coupling set yielding spin pure expansion vectors. ORB_ENER employs the sum of orbital energy approximation giving spin pure expansion vectors but usually doubles the number of Davidson iterations. EVANGELISTI uses the sums and differences of orbital energies with the SCF reference energy to produce spin pure expansion vectors. LEININGER approximation which subtracts the one-electron contribution from the orbital energies, multiplies by 0.5, and adds the one-electron contribution back in, producing spin pure expansion vectors and developed by Matt Leininger and works as well as EVANGELISTI.

• Type: string

• Possible Values: EVANGELISTI, HD_EXACT, HD_KAVE, ORB_ENER, LEININGER, Z_KAVE

• Default: EVANGELISTI