The CHAMPS Leeds group just published in the Journal of Chemical Physics two papers related to CHAMPS Work Projects 4 and 5 on quantum dynamics and nonadiabatic dynamics. In the first paper “The effect of sampling techniques used in the multiconfigurational Ehrenfest method” by C.Symonds, J.Kattitzi and D.Shalashilin (https://aip.scitation.org/doi/10.1063/1.5020567) Spin-Boson model was used to assess the samplings of Canonical Coherent States basis sets in the phase space quantum mechanics. The paper validated the sampling techniques used in our simulations of ultrafast photochemical reactions. It has been demonstrated that the techniques really work and for the Spin-Boson model the calculations converge to the exact quantum result. The Figure below shows quantum wave functions in phase space.
In the second paper “Zombie states for description of structure and dynamics of multi-electron systems” by D.Shalashilin (https://aip.scitation.org/doi/10.1063/1.5023209) a new type of Fermionic Coherent State has been introduced, which potentially can be used in simulations of nonadiabatic dynamics in chemistry and photochemistry. Fermionic Coherent States are well known in mathematics. However, they require complicated algebra of Grassmann numbers not well suited for numerical simulations in computational chemistry. The paper introduces a coherent antisymmetrised superposition of “dead” and “alive” electronic states called Zombie State (ZS), which do not need Grassmann algebra. Instead it is replaced by a very simple sign-changing rule in the definition of creation and annihilation operators. Zombie States can be used as basis functions for quantum propagation just like Canonical Coherent States for distinguishable particles. As it is shown at the Figure in standard electronic structure and dynamics theories (left frame) some spin-orbitals are occupied by electrons and some are empty. In Zombie States (right frame) all orbitals are occupied, but some electrons are more “alive” than “dead” or more “dead” than “alive”. The term “Zombie” for simultaneously “dead” and “alive” electrons was proposed by Liz Clark, Bristol School of Mathematics manager, who is acknowledged in the paper!