At. Hagler et Cs. Ewig, ON THE USE OF QUANTUM ENERGY SURFACES IN THE DERIVATION OF MOLECULAR-FORCE FIELDS, Computer physics communications, 84(1-3), 1994, pp. 131-155
This review summarizes the work in our laboratory dealing with the dev
elopment of a new class of force fields for simulating molecular prope
rties for a wide variety of practical applications. This new generatio
n of force fields, termed Class II, is based on the derivation and par
ameterization of analytic representations of quantum mechanical energy
surfaces. The energy surface is derived from a set of representative
species by systemically sampling distorted molecular structures and co
mputing the corresponding quantum mechanical energy, energy gradient a
nd Hessian matrices, i.e. the energy and its first and second derivati
ves with respect to atomic positions. This development has a number of
key implications for the development, refining and testing of molecul
ar force fields. It has been found that molecular energy surfaces are
characterized by significant anharmonic and coupling interactons. Anal
ysis of hte quantum mechanical results indicates that these effects mu
st be included in analytical representations of the force fields if ac
curate structures, energies, and dynamic properties such as vibrationa
l frequencies are to be obtained from molecular mechanics and dynamics
calculations. In addition the inclusion of such terms greatly increas
es the transferability of the force field. Such transferability is cri
tical in predicting the properties of new species not included in the
derivation of the force field, as is invariably the requirement in pra
ctical research applications. In additon it has been shown that this m
ethodology also has the pragmatic advantage of allowing for the deriva
tion of a reasonable force field based on quantum mechanics for molecu
les where little or no experimental data exist. In this report we revi
ew the methodology of developing and testing the quantum mechanically
based force fields, showing the derivation of the functional form of t
he energy expession, sampling the quantum energy surface, testing agai
nst explicit quantum results, scaling the force field to account for s
ystematic errors, and testing against experiment. We focus simultaneou
sly on criteria for establishing force field accuracy and transferabil
ity. Where possible we describe parallel comparisons with the earlier
diagonal-quadratic of Class I force fields. Finally we discuss deficie
ncies remaining in the existing level of force field development and o
utline how they may be addressed in future work.