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. There also exists a SEM debugging mode, SEMTEST. 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