Assessment of the
Electron Correlation Treatment on
the Quantum-Classical Dynamics of Retinal Protonated Schiff Base Models:
XMS-CASPT2, RMS-CASPT2, and REKS Methods
posted on 2023-11-08, 14:10authored byLeonardo Barneschi, Danil Kaliakin, Miquel Huix-Rotllant, Nicolas Ferré, Michael Filatov(Gulak), Massimo Olivucci
We compare the performance of three different multiconfigurational
wave function-based electronic structure methods and two implementations
of the spin-restricted ensemble-referenced Kohn–Sham (REKS)
method. The study is characterized by three features: (i) it uses
a small set of quantum-classical trajectories rather than potential
energy surface mapping, (ii) it focuses, exclusively, on the photoisomerization
of retinal protonated Schiff base models, and (iii) it probes the
effect of both methyl substitution and the increase in length of the
conjugate π-system. For each tested method, the corresponding
analytical gradients are used to drive the quantum-classical (Tully’s
FSSH method) trajectory propagation, including the recent multistate
XMS-CASPT2 and RMS-CASPT2 gradients. It is shown that while CASSCF,
XMS-CASPT2, and RMS-CASPT2 yield consistent photoisomerization dynamics
descriptions, REKS produces, in some of these systems, qualitatively
different behavior that is attributed to a flatter and topographically
different excited state potential energy surface. The origin of this
behavior can be traced back to the effect of the employed density
functional approximation. The above studies are further expanded by
benchmarking, at the CASSCF and REKS levels, the electronic structure
methods using a QM/MM model of the visual pigment rhodopsin.