Harmonic force field for glycine oligopeptides

The need for much more useful molecular dynamics simulations of nanosized system requires precise and unambiguous methods to determine force field parameters avoiding fitting procedures in favor of first principles ones. We use a procedure FUERZA to calculate force constant parameters for glycine oligopeptides using as an input the Hessian tensor from an ab initio calculation. For a molecular system having n atoms, The FUERZA procedure reduces the 3n X 3n problem to 3n 3 X 3 matrices representing atom-atom interactions. The procedure reproduces quite well most of the frequencies and as expected, it overestimates somehow stretching frequencies of bonds with terminal atoms such as hydrogens but it yields precise results for all other frequencies. A harmonic force field is reported for glycine oligopeptides. (C) 2007 Wiley Periodicals, Inc.