Accelerating the calculation of the rovibrational energies of tetraatomic molecules using a two-layer Lanczos algorithm

Abstract

The two-layer Lanczos algorithm has been extended to study the rovibrational spectrum of four-atom molecules in a mixed grid/finite basis representation basis. This algorithm exploits the partitioning structure of the Hamiltonian in polyspherical coordinates, and calculates the eigenstates in a reduced-dimension (RD) way but exactly. It consists of the standard Lanczos method for the outer layer iteration and the guided spectral transform (GST) Lanczos for the inner layer. For H 2CO, numerical results show that the two-layer Lanczos method is substantially efficient.