Exact quantum dynamics calculations of large dimensional molecules using phase space basis truncation

Abstract

Over the course of this project, a simple, stand-alone software code was developed, using Fortran 90 and MPI, to compute the exact vibrational spectrum of molecular systems. This code, named SwitchBLADE, is dimensionally independent and, therefore, can be used for a myriad of different molecular systems. A full theoretical analysis of what makes SwitchBLADE possible is presented---i.e., the phase space truncated symmetrized Gaussian basis and the energy truncated harmonic oscillator basis. Moreover, a full discussion of how phase space arguments can be used to better improve these truncation techniques is given. Also presented are vibrational spectra for isotropic uncoupled harmonic oscillators, coupled anharmonic oscillators, diphosphorous oxide, methyleneimine, acetonitrile, and benzene, all of which were computed using the same SwitchBLADE code. The full dynamically relevant range of states for each spectra is presented, which varies from a few hundred fordiphosphorous oxide to over one million for benzene.