Published: Aug. 19, 2024
A fundamental tenet of quantum mechanics is that properties should be independent representation. In self-consistent field methods such as density functional theory, this manifests a requirement invariant with respect to unitary transformations the occupied molecular orbitals and (separately) unoccupied orbitals. Various ad hoc measures excited-state charge separation are commonly used analyze time-dependent density-functional calculations violate requirement, they based on incoherent averages excitation amplitudes rather than over coherent superposition states. As result, these metrics afford markedly different values in various common representations including canonical orbitals, Boys-localized natural transition (NTOs). Numerical charge-transfer can unstable basis-set expansion may nonsensical presence extremely diffuse basis functions. contrast, well-defined expectation stable, representation-invariant, physically interpretable. Although NTO representation improves stability diagnostics, it remains case an average only connected value absence superposition. For satisfy condition, particle hole matrices must each dominated by single eigenvector so well described pair NTOs. Counterexamples readily found where not case.
Language: Английский