DIAG_METHOD

This specifies which method is to be used in diagonalizing the Hamiltonian. The valid options are: RSP, to form the entire H matrix and diagonalize using libciomr to obtain all eigenvalues (n.b. requires HUGE memory); OLSEN, to use Olsen’s preconditioned inverse subspace method (1990); MITRUSHENKOV, to use a 2x2 Olsen/Davidson method; and DAVIDSON (or SEM) to use Liu’s Simultaneous Expansion Method, which is identical to the Davidson method if only one root is to be found. The SEM method is the most robust, but it also requires \(2NM+1\) CI vectors on disk, where \(N\) is the maximum number of iterations and \(M\) is the number of roots.

• Type: string

• Possible Values: RSP, DAVIDSON, SEM

• Default: SEM