Natural orbitals and sparsity of quantum mutual information
(Fig.2 Representation of the H2O molecular orbitals in the frozen core approximation optimized by the algorithm. Each column corresponds to a different basis set: the first one represents the Hartree-Fock orbitals, the second one the WAHTOR-optimized orbitals and the one the natural orbitals.)
ABSTRACT:
Natural orbitals, defined in electronic structure and quantum chemistry as the (molecular) orbitals diagonalizing the one-particle reduced density matrix of the ground state, have been conjectured for decades to be the perfect reference orbitals to describe electron correlation. In the present work we applied the Wavefunction-Adapted Hamiltonian Through Orbital Rotation (WAHTOR) method to study correlated empirical ansätze for quantum computing. In all representative molecules considered, we show that the converged orbitals are coinciding with natural orbitals. Interestingly, the resulting quantum mutual information matrix built on such orbitals is also maximally sparse, providing a clear picture that such orbital choice is indeed able to provide the optimal basis to describe electron correlation. The correlation is therefore encoded in a smaller number of qubit pairs contributing to the quantum mutual information matrix.
Authors: Leonardo Ratini, Chiara Capecci, Guidoni Leonardo
Publication date: n/a (Accepted)
Journal: Journal of Chemical Theory and Computation
DOI (full article): https://doi.org/10.48550/arXiv.2308.08056