Using quantum chemistry muscle to flex massive systems: How to respond to something perturbing
In general, it is difficult to balance accuracy and computational cost in quantum chemistry calculations. One method of approaching this problem is by using classical force field methods, and another is by simplifying ab initio methods. This document discusses a merging of the two approaches, and specifically the Effective Fragment Molecular Orbital method. The fully analytic gradient for the Effective Fragment Molecular Orbital method is derived, and the implementation and accuracy are discussed. Different sets of multipole moments in the general Effective Fragment Potential method are benchmarked. Calculating the melting temperature of water using the Effective Fragment Molecular Orbital method is discussed.