Finite-Temperature, Anharmonicity, and Duschinsky Effects on the Two-Dimensional Electronic Spectra from Ab Initio Thermo-Field Gaussian Wavepacket Dynamics

Abstract

Accurate description of finite-temperature vibrational dynamics is indispensable in the computation of two-dimensional electronic spectra. Such simulations are often based on the density matrix evolution, statistical averaging of initial vibrational states, or approximate classical or semiclassical limits. While many practical approaches exist, they are often of limited accuracy and difficult to interpret. Here, we use the concept of thermo-field dynamics to derive an exact finite-temperature expression that lends itself to an intuitive wavepacket-based interpretation. Furthermore, an efficient method for computing finite-temperature two-dimensional spectra is obtained by combining the exact thermo-field dynamics approach with the thawed Gaussian approximation for the wavepacket dynamics, which is exact for any displaced, distorted, and Duschinsky-rotated harmonic potential but also accounts partially for anharmonicity effects in general potentials. Using this new method, we directly relate a symmetry breaking of the two-dimensional signal to the deviation from the conventional Brownian oscillator picture.

The hierarchy of Davydov's Ansätze and its applications

“…For example, the methodology combining TFD with the Davydov's Ansätze in Ref. 45 has been successfully applied to the simulations of nonlinear spectroscopic signals via TGA 47,247 and MCE 248 . The Davydov Ansatz methodology for the computation of nonlinear spectroscopic signals 25,59 was transferred to the MCE framework 249 .…”

Semiclassical and VSCF/VCI Calculations of the Vibrational Energies of trans- and gauche-Ethanol Using a CCSD(T) Potential Energy Surface

“… 59 − 61 AS SCIVR is a recently developed two-step procedure able to describe quantum effects starting from classical trajectories. Therefore, AS SCIVR is a member of the family of semiclassical methods (see, for instance, refs ( 62 − 70 )), and it features a characteristic way to determine the starting conditions of the semiclassical dynamics. In AS SCIVR, one starts from harmonic quantization and slowly, adiabatically, switches on the actual molecular Hamiltonian.…”

Applicability of the thawed Gaussian wavepacket dynamics to the calculation of vibronic spectra of molecules with double-well potential energy surfaces

“…This single-Hessian method was shown to be almost as accurate as the original thawed Gaussian approximation in several model and realistic systems, and was used to simulate both steady-state 74,75 and time-resolved spectra. 76,77 As in the harmonic approximation, there are different possible choices for choosing the reference Hessian, including the adiabatic and vertical Hessians of the final state or the adiabatic Hessian of the initial state (labeled "initial Hessian").…”