Surface Hopping Dynamics with the Frenkel Exciton Model in a Semiempirical Framework

Abstract

We present an implementation of the Frenkel exciton model in the framework of the semiempirical floating occupation molecular orbitals-configuration interaction (FOMO-CI) electronic structure method, aimed at simulating the dynamics of multichromophoric systems, in which excitation energy transfer can occur, by a very efficient approach. The nonadiabatic molecular dynamics is here dealt with by the surface hopping method, but the implementation we proposed is compatible with other dynamical approaches. The exciton coupling is computed either exactly, within the semiempirical approximation considered, or by resorting to transition atomic charges. The validation of our implementation is carried out on the trans -azobenzeno-2S-phane (2S-TTABP), formed by two azobenzene units held together by sulfur bridges, taken as a minimal model of multichromophoric systems, in which both strong and weak exciton couplings are present.

The Newton-X platform: new software developments for surface hopping and nuclear ensembles

“…Exciton approach for surface hopping (EXASH) 27 is a fragment-based method, where electronic properties at each timestep are derived, permuting each chromophore in the field of the others. It is set to work with semiempirical FOMO-CI and MM fields to describe systems composed of many chromophores, using an excitonic approach.…”

“…In recent years, Newton-X became the host of novel methods for nonadiabatic couplings without wavefunctions, 23 zero-point-energy leakage corrections, 24 and nonadiabatic dynamics induced by incoherent light, 25 in complex-valued potential energy surfaces, 26 and including multiple chromophores. 27 All these features, together with interfaces to numerous third-party programs spanning methods from MRCI to machine learning potentials, make Newton-X one of the richest software platforms for mixed quantum-classical simulations. This paper reviews the basic concepts underlying TSH and NEA and all these novel developments, delivering an integrated overview of the Newton-X capabilities.…”

“…The wavefunctions in eq (27) are given as the product of a Gaussian and a Hermite polynomial. One can also sample coordinates and momenta according to a Hermite function whose Gaussian exponent and center are provided by the user.…”

“…The price is that only states that can be written as linear combinations of local excitations can be considered. The first application of EXASH 27 consisted of the simulation of the dynamics of an azobenzene dimer held together by sulfur bridges. EXASH revealed that although fast, the excitation transfer between chromophores is limited to the * manifold and absent for n* states.…”

INAQS, a generic interface for non-adiabatic QM/MM dynamics: Design, implementation, and validation for GROMACS/Q-CHEM simulations

“…One may even apply ab initio exciton or fragment-based Hamiltonians. 52,[83][84][85] Thus, in general, a call to update the nuclear position should be valid across a variety of different algorithms from classical MD to ab initio MD to Ehrenfest dynamics and surface hopping. There is one difference between surface hopping and the other algorithms presented above; following Pechukas 86 and Herman, 87 in the case of a hop, the velocities of the system need to be rescaled to conserve the total energy.…”