Effective Harmonic and Anharmonic Models for Vibronic Spectra
Abstract
Vibrationally resolved spectra of medium-sized molecules contain dense progressions, weak borrowed-intensity bands and large-amplitude structural motions. Their interpretation requires state-to-state assignments together with a complete spectral envelope, while a fully anharmonic treatment of every normal coordinate is usually impractical. We introduce a general workflow that builds both outputs from automatically generated nonredundant internal coordinates and a common transition-operator representation. The harmonic level combines time-independent (TI) assignments with time-dependent (TD) thermal correlations and an explicit omitted-strength bound for the positive harmonic dipole sum. A discrete-variable representation (DVR) promotes selected flexible coordinates while the remaining modes are contracted analytically. Perturbative and variational nuclear states extend the same operator treatment to separate-state modes with Duschinsky mixing or to shared modes with residual quadratic couplings. The workflow recovers approximately 99% of the harmonic intensity for strongly reorganized medium-sized examples, reproduces measured absorption and fluorescence trends for anthracene and p-terphenyl, and gives signed electronic circular dichroism (ECD) profiles for camphor. Water photoionization, a diffuse-basis two-photon response tensor for the pyrazine n→3s Rydberg band, and nonplanar 4-pyrone calculations test continuum and anharmonic extensions. The result is a unified route from molecular structure to resolved assignments and numerically converged finite-model spectra.
Related
- Vibronic Absorption and Circular Dichroism Spectra of Chiral PDI Aggregates in Free Space and Optical Cavities
- From Ground State to Electronic and Vibronic Spectra via Memory Kernel Coupling Theory and Neural Quantum States
- AnhDis: A Scheme for Anharmonic Nuclear Ensembles and Absorption Spectra
- Assessing the performance of coupled-trajectory schemes on full-dimensional two-state linear vibronic coupling models
- Anharmonic Vibrational Structure and Bound States of the He-CO2 van der Waals Complex
BibTeX
@misc{barone2026effective,
title = {{Effective Harmonic and Anharmonic Models for Vibronic Spectra}},
author = {Vincenzo Barone},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.06457},
eprint = {2611.06457},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.06457},
}
RIS
TY - UNPB
TI - Effective Harmonic and Anharmonic Models for Vibronic Spectra
AU - Vincenzo Barone
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.06457
UR - https://arxiv.org/abs/2611.06457
AB - Vibrationally resolved spectra of medium-sized molecules contain dense progressions, weak borrowed-intensity bands and large-amplitude structural motions. Their interpretation requires state-to-state assignments together with a complete spectral envelope, while a fully anharmonic treatment of every normal coordinate is usually impractical. We introduce a general workflow that builds both outputs from automatically generated nonredundant internal coordinates and a common transition-operator representation. The harmonic level combines time-independent (TI) assignments with time-dependent (TD) thermal correlations and an explicit omitted-strength bound for the positive harmonic dipole sum. A discrete-variable representation (DVR) promotes selected flexible coordinates while the remaining modes are contracted analytically. Perturbative and variational nuclear states extend the same operator treatment to separate-state modes with Duschinsky mixing or to shared modes with residual quadratic couplings. The workflow recovers approximately 99% of the harmonic intensity for strongly reorganized medium-sized examples, reproduces measured absorption and fluorescence trends for anthracene and p-terphenyl, and gives signed electronic circular dichroism (ECD) profiles for camphor. Water photoionization, a diffuse-basis two-photon response tensor for the pyrazine n→3s Rydberg band, and nonplanar 4-pyrone calculations test continuum and anharmonic extensions. The result is a unified route from molecular structure to resolved assignments and numerically converged finite-model spectra.
ER -