This code is designed to compute a linear and nonlinear optical spectra of condensed phase systems under a range of different approximations. The two basic ways to specify a system in the code is either by constructing a generalized brownian oscillator model (GBOM) of the ground and excited state potential energy surface (PES), or by inputting a list of electronic energy gaps calculated along a molecular dynamics (MD) trajectory. A GBOM can be constructed by approximating the ground and excited state potential energy surface as harmonic around their respective minima and relating the ground and excited state normal modes through a Duschinsky rotation.
For the GBOM, a range of approximations to the linear absorption and emission spectra are implemented, ranging from Franck-Condon to second- and 3rd order cumulant approximation, as well as classical and quantum ensemble approaches and the hybrid E-ZTFC method. If the model is constructed from an MD trajectory input, only cumulant and ensemble spectra can be computed.
For nonlinear spectroscpy, only transient absorption and 2DES are implemented so far. When using an MD trajectory, nonlinear spectra can be generated using the second- or 3rd order cumulant approach. When using a GBOM Hamiltonian as input, spectra can either be generated using the cumulant method, or using an exact closed-form expression of the finite temperature nonlinear response function derived by us recently (FC2DES, see below).
The module computing Franck-Condon spectra for a GBOM is based on the algorithm outlined in B. de Souza, F. Neese, and R. Izsak, J. Chem. Phys. 148, 034104 (2018). An extension of the formalism to nonlinear spectroscopy (FC2DES) was developed recently by us and is outlined in L. Allan, and T. J. Zuehlsdorff, J. Chem. Theory Comput. 21, 5625-5621 (2025)
The cumulant solutions of the GBOM, as well as the third order cumulant approximation as applied to systems sampled from MD trajectories are detailed in T. J. Zuehlsdorff, A. Montoya-Castillo, J. A. Napoli, T. E. Markland, and C. M. Isborn, J. Chem. Phys. 151, 074111 (2019); L. Allan, and T. J. Zuehlsdorff, J. Chem. Phys. 160, 074108 (2024) for linear spectroscopy and T. J. Zuehlsdorff, H. Hong, L. Shi, and C. M. Isborn, J. Chem. Phys. 153, 044127 (2020) for nonlinear spectroscopy. An extension of the Cumulant formalism to account for non-Condon effects through dipole moment fluctuations was developed in Z. R. Wiethorn, K. E. Hunter, T. J. Zuehlsdorff, and A.-M. Castillo, J. Chem. Phys. 59, 244114 (2023).
The theoretical underpinnings of hybrid approaches such as the E-ZTFC method are described in the following references: T. J. Zuehlsdorff, and C. M. Isborn, J. Chem. Phys. 148, 024110 (2018), T. J. Zuehlsdorff, J. A. Napoli, J. M. Milanese, T. E. Markland, and C. M. Isborn, J. Chem. Phys. 149, 024107 (2018), T. J. Zuehlsdorff, A. Montoya-Castillo, J. A. Napoli, T. E. Markland, and C. M. Isborn, J. Chem. Phys. 151, 074111 (2019).
Parts of the interface allowing for the construction of the GBOM from TeraChem (http://www.petachem.com/products.html) output files are based on code written by Ajay Khanna. The implementation of "tamed" third order cumulant contributions, as well as a formultion of nonlinear spectroscopy for GBOM Hamiltonians was carried out by Lucas Allan.
Copyright (C) 2019-2025 Tim J. Zuehlsdorff (zuehlsdt@oregonstate.edu)
The source code is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Mozilla Public License, v. 2.0, for more details.