Hello,
Some programs for molecular mechanics/dynamics truncate non-bonded interactions and (due to asymptotic nature of Lennard-Jones and Coulomb potentials) set them to zero between atoms that are further than chosen cutoff distance. For example Namd use such scheme: https://www.ks.uiuc.edu/Research/namd/2.12/ug/node23.html . I want to ask if Q-Chem also use such truncation scheme in QM/MM calculations for MM part or just “calculate everything”?
Tiopirfur
Those cutoffs (which need to be implemented with smooth cutoffs, by the way) can be important to reducing the cost in very large MD simulations under periodic boundaries. For the types of calculations you’re going to run with Q-Chem, the QM cost will dominate everything so there’s vanishingly little savings to be had in truncating the LJ interactions. Thus, no such option exists to the best of my knowledge.