A simplified charge projection scheme for long-range electrostatics in ab initio QM/MM calculations

Xiaoliang Pan, Kwangho Nam, Evgeny Epifanovsky, Andrew C. Simmonett, Edina Rosta, Yihan Shao
2021 Journal of Chemical Physics  
In a previous work [Pan et al., Molecules 23, 2500 (2018)], a charge projection scheme was reported, where outer molecular mechanical (MM) charges [>10 Å from the quantum mechanical (QM) region] were projected onto the electrostatic potential (ESP) grid of the QM region to accurately and efficiently capture long-range electrostatics in ab initio QM/MM calculations. Here, a further simplification to the model is proposed, where the outer MM charges are projected onto inner MM atom positions
more » ... ead of ESP grid positions). This enables a representation of the long-range MM electrostatic potential via augmentary charges (AC) on inner MM atoms. Combined with the long-range electrostatic correction function from Cisneros et al. [J. Chem. Phys. 143, 044103 (2015)] to smoothly switch between inner and outer MM regions, this new QM/MM-AC electrostatic model yields accurate and continuous ab initio QM/MM electrostatic energies with a 10 Å cutoff between inner and outer MM regions. This model enables efficient QM/MM cluster calculations with a large number of MM atoms as well as QM/MM calculations with periodic boundary conditions.
doi:10.1063/5.0038120 pmid:33445891 pmcid:PMC7808763 fatcat:2jjebdd5f5bsrhf7pb6whctjni