Long-range behavior of natural orbitals and electron density

1976 ◽  
Vol 64 (6) ◽  
pp. 2707 ◽  
Author(s):  
Mel Levy
Keyword(s):  
Electron Density ◽  
Long Range ◽  
Natural Orbitals

Pseudo‐eigenvalue equation for natural orbitals of two‐electron systems and long range behavior

1979 ◽  
Vol 70 (12) ◽  
pp. 5919-5921 ◽  
Author(s):  
Harris J. Silverstone ◽  
Dennis P. Carroll ◽  
Robert Melville Metzger
Keyword(s):  
Long Range ◽  
Eigenvalue Equation ◽  
Electron Systems ◽  
Natural Orbitals

scholarly journals Representation of the QM Subsystem for Long-Range Electrostatic Interaction in Non-Periodic Ab Initio QM/MM Calculations

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2500 ◽  
Author(s):  
Xiaoliang Pan ◽  
Edina Rosta ◽  
Yihan Shao
Keyword(s):  
Electron Density ◽  
Long Range ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Switching Function ◽  
Excitation Energies ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Distance Cutoff ◽  
Switching Functions

In QM/MM calculations, it is essential to handle electrostatic interactions between the QM and MM subsystems accurately and efficiently. To achieve maximal efficiency, it is convenient to adopt a hybrid scheme, where the QM electron density is used explicitly in the evaluation of short-range QM/MM electrostatic interactions, while a multipolar representation for the QM electron density is employed to account for the long-range QM/MM electrostatic interactions. In order to avoid energy discontinuity at the cutoffs, which separate the short- and long-range QM/MM electrostatic interactions, a switching function should be utilized to ensure a smooth potential energy surface. In this study, we benchmarked the accuracy of such hybrid embedding schemes for QM/MM electrostatic interactions using different multipolar representations, switching functions and cutoff distances. For test systems (neutral and anionic oxyluciferin in MM (aqueous and enzyme) environments), the best accuracy was acquired with a combination of QM electrostatic potential (ESP) charges and dipoles and two switching functions (long-range electrostatic corrections (LREC) and Switch) in the treatment of long-range QM/MM electrostatics. It allowed us to apply a 10Å distance cutoff and still obtain QM/MM electrostatics/polarization energies within 0.1 kcal/mol and time-dependent density functional theory (TDDFT)/MM vertical excitation energies within 10−3 eV from theoretical reference values.

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