Conformational dynamics of an alanine dipeptide analog: An ab initio molecular dynamics study

An ab initio molecular dynamics (MD) simulation technique employing the Born-Oppenheimer approach in the framework of a Gaussian implementation of Kohn-Sham density functional theory is used to study the gas-phase conformational dynamics of an alanine dipeptide analog. It is found that conformational transformation between $C5\mathrm{}$ and ${C7\mathrm{}}_{\mathrm{eq}}$ occurs on the picosecond time scale. Classical MD simulations using most of the popular force fields do not yield a transition even after nanoseconds. An analysis is given of the difference, for this small gas-phase system, between ab initio MD and traditional MD simulation using force fields.