Maitreyee Sarkar | Searcharxiv

arXiv2026

Computing Reaction and Activation Energies of Pericyclic Reactions using a Symmetry-Adapted VQE Algorithm

Pericyclic reactions provide stringent tests for quantum simulations because their mechanisms are governed by orbital symmetry and involve correlated transition states. In this work, we employ the variational quantum eigensolver (VQE) combined with a previously established symmetry-guided active-space selection protocol based on symmetry-matched fractions (SMF-VQE) to simulate Diel-Alder and Alder-ene reactions in complex systems involving extended pi-conjugation and multiple bonding. Although absolute electronic energies obtained from the current protocol exhibit significant deviations from the values computed using CCSD method, the symmetry-guided active spaces yield substantial cancellation of deviations in the energy differences. As a result, reaction energies are predicted with error (relative to CCSD) less than one kcal per mol, while activation energies are reproduced within about five to six kcal per mol. The symmetry-guided protocol also reduces the large combinatorial space of active-space choices to a single symmetry-consistent selection for each reaction.

physics.chem-ph↗

arXiv2025

Quantum Simulations of Chemical Reactions: Achieving Accuracy with NISQ Devices

Quantum computing is viewed as a promising technology because of its potential for polynomial growth in complexity, in contrast to the exponential growth observed in its classical counterparts. In the current Noisy Intermediate-Scale Quantum (NISQ) era, the Variational Quantum Eigensolver (VQE), a hybrid variational algorithm, is utilized to simulate molecules using qubits and calculate molecular properties. However, simulating a chemical reaction to compute the reaction energy using VQE algorithm has not yet reached chemical accuracy relative to the benchmark computational chemistry methods due to limitations such as the number of qubits, circuit depth, and noise introduced within the model. To address this issue, we propose the definition of different active spaces for studying chemical reactions, incorporating irreducible representations of both the ground and excited states of the molecules. Our results demonstrate that this approach achieves chemical accuracy in predicting the reaction energy for various reactions. For all reactions studied, the difference in reaction energies between conventional computational chemistry methods and the quantum-classical hybrid VQE algorithm is less than 1 kcal/mol. Furthermore, our analysis simplifies the process of selecting active spaces and electrons for each reaction, reducing it to a single optimal combination that ensures the chemical accuracy for each reaction.

physics.chem-ph↗