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Why Do Mixed Quantum-Classical Methods Describe Short-Time Dynamics through Conical Intersections So Well? Analysis
Rami Gherib1,2, Ilya G Ryabinkin1,2, Artur F Izmaylov1,2
1Department of Physical and Environmental Sciences, University of Toronto Scarborough , Toronto, Ontario M1C 1A4, Canada.
Journal of Chemical Theory and Computation
|November 18, 2015
Summary
Popular mixed quantum-classical methods effectively mimic geometric phase effects in nonadiabatic dynamics, despite lacking nuclear wave functions. These methods accurately reproduce ultrafast interstate crossing dynamics, crucial for simulating conical intersections.
Area of Science:
- Quantum dynamics
- Chemical physics
- Computational chemistry
Background:
- Simulating nonadiabatic dynamics through conical intersections necessitates including the geometric phase (GP).
- Standard mixed quantum-classical (MQC) methods like surface hopping and Ehrenfest neglect the nuclear wave function, precluding GP incorporation.
- Despite this limitation, MQC methods often accurately predict ultrafast interstate crossing dynamics.
Purpose of the Study:
- To investigate how MQC methods effectively reproduce dynamical geometric phase effects.
- To elucidate the mechanisms by which MQC methods mimic GP impacts on nonadiabatic dynamics.
Main Methods:
- Utilized two-dimensional linear vibronic coupling models.
- Compared MQC simulations (surface hopping, Ehrenfest) with exact quantum propagation.
- Analyzed the compensation of nonadiabatic couplings and transfer enhancement effects.
Main Results:
- MQC methods effectively compensate for repulsive diagonal second-order nonadiabatic couplings.
- MQC methods enhance the transfer of a cylindrically symmetric nuclear distribution component.
- The study reveals how MQC methods implicitly capture significant GP effects.
Conclusions:
- MQC methods, while not explicitly including GP, can effectively mimic its crucial dynamical consequences.
- The findings explain the surprising accuracy of MQC methods in simulating nonadiabatic dynamics at conical intersections.
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