Accurate vibrational energy levels of the simplest Criegee intermediate (CH2OO) were determined on a recently developed ab initio based nine-dimensional potential energy surface using three quantum mechanical methods. the first is the iterative Lanczos method using a conventional basis expansion with an exact Hamiltonian. the second and more efficient method is the multi-configurational time-dependent Hartree (MCTDH) method in which the potential energy surface is refit to conform to the sums-of-products requirement of MCTDH. Finally, the energy levels were computed with a vibrational self-consistent field/virtual configuration interaction method in MULTIMODE. the low-lying levels obtained from the three methods are found to be within a few wave numbers of each other, although some larger discrepancies exist at higher levels. the calculated vibrational levels are very well represented by an anharmonic effective Hamiltonian.
- Calculations,
- Hamiltonians,
- Molecular physics,
- Potential energy,
- Potential energy surfaces,
- Quantum chemistry,
- Quantum theory,
- Vibrations (mechanical),
- Configuration interaction method,
- Criegee intermediates,
- Effective Hamiltonian,
- Iterative Lanczos method,
- Multimode calculations,
- Quantum mechanical method,
- Self-consistent field,
- Vibrational energy levels,
- Iterative methods
Available at: http://works.bepress.com/richard_dawes/109/