Chemical Reactions in the Framework of Single Quantum Systems

Raymond Daudel, Bernard Pullman

M R Nirmal, Sarkar, Shampa, Manoj Karunakaran Nambiar +1 more

A lot of progress has been made in recent times for simulating accurately the ground state energy of small molecules and their potential energy surface, using quantum-classical hybrid computing architecture. While these single point energy calculations are a significant milestone for quantum chemistry simulation on quantum hardware, a similarly important application is to trace accurately the reaction pathway of various chemical transformations. Such computations require accurate determination of the equilibrium or lowest energy molecular geometry, either by computing energy gradients with respect to the molecule's nuclear coordinates or perturbative distortion of the molecular configuration. In this work, we present a modular quantum-classical hybrid framework, to accurately simulate chemical reaction pathway of various kinds of molecular reactions. We demonstrate our framework by accurately tracing the isomerization pathway for small organic molecules. This framework can now be readily applied to study other 'active' molecules from the pharma and chemical industries.

Maitreyee Sarkar, Lisa Roy, Akash Popat Gutal +2 more

Simulation of chemical reactions to compute reaction energies using variational algorithms remains challenging in achieving chemical accuracy relative to benchmark computational chemistry methods due to limitations such as qubit number, circuit depth, and noise. To address this issue, we propose the definition of different active spaces for studying chemical reactions, incorporating irreducible representations of both ground and excited states by defining the maximum contribution of excitation terms in the ansatz, implemented here within a second-order Trotterized UCCSD-VQE framework. Our results demonstrate that this approach can achieve chemical accuracy for several representative reactions and yields close agreement with benchmark methods across a broader range of reactions. For all reactions studied, the difference in reaction energies between VQE and CCSD remains within 1 kcal/mol. At the same time, comparison with FCI shows chemical accuracy for several cases and close agreement for the remaining systems. Furthermore, our analysis simplifies the selection of active spaces and electrons for each reaction, reducing it to a single optimal combination that supports chemically accurate or near-chemical-accuracy predictions.

Jean‐Louis Calais, Eugene S. Kryachko

Jincheng Zhang

Quantum-Enhanced Simulation of Complex Chemical Reactions (Q-Chem) is a novel approach to molecular dynamics simulation designed to overcome the limitations of current methods, particularly when simulating complex chemical reactions. This paper introduces a new method leveraging quantum entanglement to model the intricate interactions between molecules, aiming to achieve unprecedented accuracy and resolution in capturing reaction dynamics. The core mechanism centers around incorporating quantum entanglement into the molecular dynamics framework to represent and simulate the correlations within chemical pathways, offering a pathway to accurately model reactions that are currently intractable using traditional methods. The paper details the theoretical framework, implementation of the quantum-enhanced molecular dynamics simulation, and preliminary results demonstrating its potential for significantly improved simulations of complex chemical reactions.

Lutz Dieter Künne