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Molecular Quantum Dynamics

The quantum effects of zero point motion, tunnelling and coherence influence molecular dynamics, reactivity and thermodynamic properties, as well as determining the lineshapes of various absorption and emission spectra. We have developed and applied novel methods for simulating quantum molecular dynamics in both the gas and condensed phases.

Ro-vibrational Wavefunctions

Fluxional dynamics in molecules with tunnelling assisted conformational change leads to complicated ro-vibrational spectra that are hard to interpret. We have developed methods based on Variational Configuration Interaction, Perturbation Theory and Diffusion Monte Carlo theories, targetting the accurate first principles calculation and interpretation of ro-vibrational spectra of fluxional molecules, treating isomerisation dynamics through special curvilinear coordinate systems.

Potential Energy Surfaces

On-the-fly evaluation of the Born-Oppenheimer potential energy surface can be avoided if a suitable analytic form of the PES can be obtained through machine learning. We have developed a powerfull approach that utilises the LASSO machine learning method to construct well behaved model potential surfaces that reproduce the electronic potential to high fidelity.

Papers

  • Viglaska, Wang, Carrington Jr, Tew. Computational study of the rovibrational spectrum of H2O-HF. J. Mol. Spectrosc. 384, 111587 (2022) — computes rovibrational energy levels, transition frequencies, and intensities using a new ab initio PES and compares them with available experimental data.
  • Erfor, Tschope, Rauhut, Tew. Ab initio calculation of rovibrational states for non-degenerate double-well potentials: cis–trans isomerization of HOPO. J. Chem. Phys. 152, 174306 (2020) — uses vibrational configuration interaction to computes rovibrational spectra of metaphosphorous acid accouting for tunnelling effects of the torsional mode.
  • Mizukami, Tew. Ab Initio Vibrational Spectroscopy of cis- and trans-Formic Acid from a Global Potential Energy Surface. J. Phys. Chem. A 120, 9815 (2016) — vibrational configuration interaction calculations on a Lasso machine learned 9D PES reveal the fermi-resonance of the torsional mode was incorrecly assigned.
  • Mizukami, Habershon, Tew. A compact and accurate semi-global potential energy surface for malonaldehyde from constrained least squares regression. J. Chem. Phys. 141, 144310 (2014) — develops a Lasso machine learning approach to model a 21D PES and uses importance sampled DMC to show the zero-point tunnelling splitting agrees to within 1 wavenumber of experiment.