This work introduces a methodology for performing anharmonic vibrational structure calculations that can be deployed in a hybrid, quantum-classical mode and demonstrates a hybrid, quantum-classical computational workflow, in which a quantum sampling algorithm provides the seed.
Abstract
Quantum-centric workflows are a promising route to improving the accuracy of property predictions in computational chemistry and materials science. By integrating quantum sampling algorithms with classical solvers, electronic structure calculations have recently demonstrated their potential even on noisy intermediate-scale quantum devices. In principle, the method of Vibrational Configuration Interaction (VCI) is suitable for integration with quantum sampling algorithms as well. However, demonstrations of computational workflows for quantum-centric, vibrational property predictions are still lacking. Here, we introduce a methodology for performing anharmonic vibrational structure calculations that can be deployed in a hybrid, quantum-classical mode. Starting from a quartic force field, the approach combines a Vibrational Self-Consistent Field (VSCF) with VCI in either Full, Selected (S-VCI), or Symmetry-Adapted (SA-VCI) mode. In S-VCI, an Epstein-Nesbet perturbative screening significantly reduces the configuration space while retaining high predictive accuracy. A state-list input enables the integration of externally generated vibrational configurations as a seed space. As a proof-of-concept, we demonstrate a hybrid, quantum-classical computational workflow, in which a quantum sampling algorithm provides the seed. Our vibrational wave function analysis package ViBra, equipped with a graphical interface, is available at https://github.com/raphafe96/ViBra.
This work shows that SQD performance can be strongly influenced by uncontrolled growth of the classical diagonalization subspace, and establishes measurement-basis engineering as a promising route to improving quantum sampling methods for electronic structure.
Connor van Rossum, J. Cohn, Sally Shrapnel et al.· 2 citations
This work performs excited-state molecular dynamics simulations of the formaldimine molecule by combining the surface hopping nonadiabatic molecular dynamics technique with quantum algorithms, and evaluates the accuracy and feasibility of three different gradient calculation approaches integrated with the quantum computing components.
Silvia Riera-Villapún, Jaime Scharfhausen-Curiel, J. L. Sánchez Toural et al.· Journal of Physical Chemistr...· 0 citations
The present work revisits the methods within CP2K that turn electronic structure into dynamics, transport, and spectroscopic response, highlighting CP2K's unique capability to unify quantum chemistry with quantum and statistical mechanics within a versatile, holistic simulation environment.
Jan Wilhelm, Anna-Sophia Hehn, Hossam Elgabarty et al.· 1 citation· ⚡1
Conical intersections (CIs) are primary pathways for ultrafast nonradiative relaxation in photoexcited molecules, yet their spectroscopic signatures often reflect a complex interplay of electronic motion, vibrational dynamics, and environmental dephasing. This challenge becomes particularly significant when the nuclear coordinate driving the relaxation is strongly anharmonic, since harmonic approximations commonly employed in CI models cannot capture the asymmetric level structure and wave-packet evolution associated with realistic bondstretching motion. Here, we develop a dissipative two-state, two-mode vibronic model that combines an anharmonic Morse tuning coordinate with a harmonic coupling coordinate and a three-level extension for simulating two-dimensional electronic–vibrational (2DEV) spectroscopy. Reduced density-matrix dynamics are propagated using the hierarchy equations of motion, while absorptive 2DEV spectra are calculated within a phase-matching formalism. To isolate the effect of Morse anharmonicity, we further introduce a parameter-matched fully harmonic reference model with the same local frequencies, potential-surface displacements, electronic coupling, bath parameters, temperature, and initial conditions. The resulting potential-energy surfaces generate an asymmetric branching space in which the same nonadiabatic dynamics appear as rapid population transfer in the adiabatic representation and as a more gradual redistribution in the diabatic representation. The calculated dynamics exhibit coherent oscillations with a dominant component near 620 cm
−1
, while the 2DEV spectra reveal time-dependent redistribution of vibronic intensity during passage through the intersection region. Unequal vibronic peak spacings and evolving center-line slopes emerge as experimentally testable signatures of anharmonic vibronic coupling and changing electronic-vibrational correlation within the present model. These results demonstrate that anharmonic Morse-based models qualitatively alter how CI dynamics appear in 2DEV spectroscopy.
Jing-Wen Li, Qiang Zhang, Pan-Pan Zhang et al.· Chinese Physics B· 0 citations
Experiments indicate that collective coupling of molecular ensembles to confined optical modes can modify excited-state dynamics and photochemical reactivity. To describe such cavity-induced effects at atomic resolution, semi-classical molecular dynamics approaches have been developed that treat nuclear motion classically while describing the collective light-matter interaction within the Tavis-Cummings framework of quantum electrodynamics. Here, we benchmark mixed quantum-classical approaches, Ehrenfest dynamics, and Fewest-Switches Surface Hopping (FSSH) for simulating nonadiabatic dynamics of electronically strongly coupled carbon monoxide molecules. Their predictions are compared against numerically exact quantum dynamics simulations performed with the multi-configuration time-dependent Hartree method, which treats both electronic and nuclear degrees of freedom quantum mechanically. We find that the semi-classical approaches reproduce the qualitative features of the full quantum dynamics. Quantitative agreement is best achieved with FSSH when a decoherence correction is included. These results demonstrate that mixed quantum-classical methods provide a computationally efficient and quantitatively reliable alternative to fully quantum simulations for investigating nonadiabatic photochemistry under collective electronic strong coupling in systems beyond the reach of exact quantum treatments.
Arun Kumar Kanakati, Oriol Vendrell, G. Groenhof· Journal of Chemical Physics· 0 citations
High-accuracy molecular quantum chemistry offers a promising toolbox for applications to condensed-phase systems, but this field is difficult to enter due to its combination of topics from molecular quantum chemistry, solid-state physics, and numerical methods. Aiming to ease this transition, we present a comprehensive, pedagogical tutorial on periodic quantum chemistry calculations, using both mean-field and correlated theories. The subtleties of periodic Coulomb interactions are discussed in detail, focusing on the Ewald summation approach. We describe the two most popular periodic, one-electron basis functions---plane waves and periodic linear combinations of atomic orbitals---and we give formulas for all Hamiltonian integrals. Next, we explain the use of $k$-point sampling as a symmetry adaptation of supercell basis functions and the associated savings in computational costs as well as the use of density fitting and related approximations to further reduce costs. We present the working equations of a few example periodic quantum chemistry methods, including Hartree-Fock theory, perturbation theory, and coupled-cluster theory, and we discuss their finite-size errors and convergence to the physically relevant thermodynamic limit. Finally, we briefly discuss local correlation and quantum embedding theories, which are especially appropriate for periodic systems due to their lattice translational symmetries.
H. Ye, Timothy C. Berkelbach· 1 citation
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