Quantum simulations of molecular systems with intrinsic atomic orbitals

Quantum simulations of molecular 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 in quantum simulations of molecules to improve the accuracy of energies and properties at the same computational cost required by a minimal basis. 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-state energies of small molecules by a combination of quantum algorithms using IBM quantum computers.