Quantum mechanics/extremely localized molecular orbital embedding technique: Theoretical foundations and further validation

Embedding techniques are nowadays considered the go-to-methods to have an optimal trade-off between chemical accuracy and computational cost in modeling large molecular systems. Several efficient strategies of this kind have been developed over the years, from QM/MM (quantum mechanics/molecular mechanics) techniques to more recent and promising density functional theory embedding approaches. Along this line, we have recently proposed the QM/ELMO (quantum mechanics/extremely localized molecular orbital) method. This strategy describes the chemically important region of an extended system at a fully quantum mechanical (QM) level, while the rest is treated through frozen extremely localized molecular orbitals (ELMOs) properly transferred from recently assembled libraries or ad hoc model molecules. In this work, after reviewing the theoretical bases of the novel technique, we will show and discuss the results of further validation tests, with a particular focus on basis set dependence and computational cost.