(284f) Extending a Linear Basis Function Approach to Alchemically Solvating Charged Particles and Changing Atomic Identity

Authors: 
Naden, L. N., University of Virginia
Shirts, M. R., University of Virginia

Our linear basis function approach is an efficient tool for inserting or removing atomic
sites in free energy calculations. We have previously shown how splitting the potential
energy function into a sum of pairs of basis functions, which depend only on
coordinates, and alchemical switches, which depend only on the
coupling variable can minimize the variance and statistical error of alchemical solvation.
Here we present the optimal alchemical switch and basis functions for solvating charged
particles in dense fluid. The most optimal sequence of nonbonded forces to alchemically
couple to the environment is also examined to further reduce statistical error.

Changes in chemical identity at a fixed atomic site are also examined with the linear basis
function approach. The basis function approach allows predicting the free energy surface
across a wide range of nonbonded properties requiring very minimal sampling across the
entire surface. The basis function approach removes the need to re-run the inner force
loop of the simulation package at every point of the free energy surface and can be run
entirely in post-processing. This is done only with Lennard-Jones spheres as changing
identity often requires geometry changes in bonded molecules, which we do not explore.
This formalism can accelerate future nonbonded parameterizations.

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