Quantum simulations of molecular systems with intrinsic atomic orbitals

Abstract

Quantum simulations of quantum chemistry systems on quantum computers often employ minimal basis sets of Gaussian orbitals. In comparison with more realistic basis sets, quantum simulations employing minimal basis sets require fewer qubits and quantum gates, but yield results of lower accuracy. A natural strategy to achieve more accurate results is to increase the basis set size, which in turn requires increasing the number of qubits and quantum gates. Here we explore the use of intrinsic atomic orbitals (IAOs) in quantum simulations of molecules, to improve the accuracy of energies and properties at the same computational cost required by a minimal basis. Focusing on the cleavage of the N-H bond in ammonia as a use case, we investigate ground-state energies and one- and two-body density operators in the framework of the variational quantum eigensolver, employing and comparing different Ansatze. We also demonstrate the use of this approach in the calculation of ground- and excited-states energies of the NH$_{3}$ molecule by a combination of quantum algorithms, using IBM Quantum computers.