Electric Field Gradient Calculations for Ice VIII and IX using Polarizable Embedding: A Comparative Study on Classical Computers and Quantum Simulators

TL;DR

This study evaluates the PE-VQE-SCF quantum algorithm for calculating electric field gradients in ice phases, demonstrating its accuracy and discussing the impact of environmental inclusion and basis set size on quantum computational complexity.

Contribution

It introduces and tests the PE-VQE-SCF method for electric field gradient calculations, comparing its performance with traditional methods and experiments.

Findings

PE-VQE-SCF results match experimental data within uncertainties.

Including environment is crucial for accurate electric field gradient calculations.

Environmental effects increase the complexity of quantum wavefunction optimization.

Abstract

We test the performance of the Polarizable Embedding Variational Quantum Eigensolver Self-Consistent-Field (PE-VQE-SCF) model for computing electric field gradients with comparisons to conventional complete active space self-consistent-field (CASSCF) calculations and experimental results. We compute quadrupole coupling constants for ice VIII and ice IX. We find that the inclusion of the environment is crucial for obtaining results that match the experimental data. The calculations for ice VIII are within the experimental uncertainty for both CASSCF and VQE-SCF for oxygen and lie close to the experimental value for ice IX as well. With the VQE-SCF, which is based on an Adaptive Derivative-Assembled Problem-Tailored (ADAPT) ansatz, we find that the inclusion of the environment and the size of the different basis sets do not directly affect the gate counts. However, by including an explicit environment, the wavefunction and, therefore, the optimization problem becomes more complicated, which usually results in the need to include more operators from the operator pool, thereby increasing the depth of the circuit.