iSPECTRON: A simulation interface for linear and nonlinear spectra with ab‐initio quantum chemistry software

Abstract

We introduce iSPECTRON, a program that parses data from common quantum chemistry software (NWChem, OpenMolcas, Gaussian, Cobramm, etc.), produces the input files for the simulation of linear and nonlinear spectroscopy of molecules with the Spectron code, and analyzes the spectra with a broad range of tools. Vibronic spectra are expressed in term of the electronic eigenstates, obtained from quantum chemistry computations, and vibrational/bath effects are incorporated in the framework of the displaced harmonic oscillator model, where all required quantities are computed at the Franck-Condon point. The program capabilities are illustrated by simulating linear absorption, transient absorption and two dimensional electronic spectra of the pyrene molecule. Calculations at two levels of electronic structure theory, time-dependent density functional theory (with NWChem) and RASSCF/ RASPT2 (with OpenMolcas) are presented and compared where possible. The iSPECTRON program is available online at https://github.com/ispectrongit/ iSPECTRON/ and distributed open source under the terms of the Educational Community License version 2.0 (ECL 2.0).

In Silico Ultrafast Nonlinear Spectroscopy Meets Experiments: The Case of Perylene Bisimide Dye

“…31 The information flow from the QC codes to Spectron, as well as the analysis and plotting of the obtained spectroscopic data, is managed through the recently developed iSPECTRON interface. 10 Reference 10 also contains details about Spectron functioning, inputs, and parameters.…”

“…The reliability of simulations to support the interpretation of experimental signals and furnish a microscopic understanding of the studied molecular systems is grounded on an accurate description of the molecular electronic structure and a simple and robust model for the spectroscopic technique, able to provide connection with the experimentally measured observables. 10 Accurate electronic structure calculations can be obtained from a wide range of methodologies, some of which are readily available in standard quantum chemistry (QC) packages. In theoretical nonlinear spectroscopy studies, the electronic structure is usually obtained from multireference methods, such as the restricted active space self-consistent-field (RASSCF) and its second-order perturbation theory variant (RASPT2) due to their universal and potentially accurate treatment of highly excited states required for simulating TA/ 2DES features.…”

“…The reliability of simulations to support the interpretation of experimental signals and furnish a microscopic understanding of the studied molecular systems is grounded on an accurate description of the molecular electronic structure and a simple and robust model for the spectroscopic technique, able to provide connection with the experimentally measured observables . Accurate electronic structure calculations can be obtained from a wide range of methodologies, some of which are readily available in standard quantum chemistry (QC) packages.…”

Near-Ultraviolet Circular Dichroism and Two-Dimensional Spectroscopy of Polypeptides

“…Transport between excitons was neglected (due to the very small coupling between sites): by virtue of this assumption, the line-shape of the obtained 2DUV maps is exact [46]. A concise summary of the relation between ab initio data and 2DUV spectra is being reported elsewhere [47]. A sample of the SPECTRON input used is given in the SI.…”

Computational spectroscopy of complex systems

“…Therefore, special techniques have been developed to predict excited state solvent shifts 26,27 of molecules in the condensed phase and couplings 28,29 between those at a speed sufficient enough to be used in quantum-classical response function based spectral calculations. 30,31 Such calculations provide the possibility of predicting and interpreting advanced spectroscopies as two-dimensional (2D) infrared 32 and electronic spectroscopies 33 of complex systems containing tens or even hundreds of chromophores. 34,35 This kind of computational spectroscopy of complex systems is needed for the interpretation of experimental spectra, design of new materials, and prediction of spectral properties.…”