Calculating Vibrational Excited State Absorptions with Excited State Constrained Minimized Energy Surfaces

Abstract

The modeling and interpretation of vibrational spectra are crucial for studying reaction dynamics using vibrational spectroscopy. Most prior theoretical developments focused on describing fundamental vibrational transitions while fewer developments focused on vibrational excited state absorptions. In this study, we present a new method that uses excited state constrained minimized energy surfaces (CMESs) to describe vibrational excited state absorptions. The excited state CMESs are obtained similarly to the previous ground state CMES development in our group but with additional wave function orthogonality constraints. Using a series of model systems, including the harmonic oscillator, Morse potential, double-well potential, quartic potential, and two-dimensional anharmonic potential, we demonstrate that this new procedure provides good estimations of the transition frequencies for vibrational excited state absorptions. These results are significantly better than those obtained from harmonic approximations using conventional potential energy surfaces, demonstrating the promise of excited state CMES-based methods for calculating vibrational excited state absorptions in real systems.

Vibrational Spectra of Highly Anharmonic Water Clusters: Molecular Dynamics and Harmonic Analysis Revisited with Constrained Nuclear-Electronic Orbital Methods

“…The CNEO-MD framework was recently developed by our group to incorporate nuclear quantum effects, especially zero-point effects due to quantum delocalization, in practical molecular simulations . Its working equations are ,, m d ⟨ bold-italicx ⟩ normald t = false⟨ bold-italicp false⟩ and d ⟨ bold-italicp ⟩ normald t ≈ prefix− ∇ ⟨ bold-italicx ⟩ V normalC normalN normalE normalO ( ⟨ x ⟩ ) where ⟨ x ⟩ and ⟨ p ⟩ are expectation values of nuclear position and momentum operators, respectively, and V CNEO (⟨ x ⟩) is the CNEO-DFT energy surface. Note that CNEO-MD is essentially an AIMD method using the energies and gradients of CNEO-DFT computed on-the-fly at each MD step.…”

“…The CNEO-MD framework was recently developed by our group to incorporate nuclear quantum effects, especially zero-point effects due to quantum delocalization, in practical molecular simulations. 44 Its working equations are 43,44,49 x p m t…”

Early-Career and Emerging Researchers in Physical Chemistry Volume 2

“…The authors show that, by using a ML architecture that is largely invariant to the conformational properties, the model can predict the reorganization energies of the most stable conformers based only on approximate three-dimensional structures, thus eliminating the need for costly candidate structure optimization. Next, Yang and co-workers discuss a new way to simulate absorption from vibrationally excited states using so-called constrained minimized energy surfaces. Tests on several different types of oscillators, including those with high anharmonicities, indicate excellent performance of the method.…”

Transition State Theory within Constrained Nuclear-Electronic Orbital Framework: Accurate Hydrogen Atom Transfer Reaction Rates with Direct Incorporation of Quantum Nuclear Delocalization Effects

“…Here in this paper, we will integrate our recently developed constrained nuclear-electronicorbital (CNEO) framework [53][54][55][56][57][58][59][60] with the conventional TST to calculate HAT reaction rate constants. We will show that even without the VTST treatment or the tunneling correction, this new method, dubbed CNEO TST, can accurately predict the HAT rate constants, especially at the ambient temperature.…”