  We present an ab initio approach for evaluating a free energy profile along a
reaction coordinate by combining logarithmic mean force dynamics (LogMFD) and
first-principles molecular dynamics. The mean force, which is the derivative of
the free energy with respect to the reaction coordinate, is estimated using
density functional theory (DFT) in the present approach, which is expected to
provide an accurate free energy profile along the reaction coordinate. We apply
this new method, first-principles LogMFD (FP-LogMFD), to a glycine dipeptide
molecule and reconstruct one- and two-dimensional free energy profiles in the
framework of DFT. The resultant free energy profile is compared with that
obtained by the thermodynamic integration method and by the previous LogMFD
calculation using an empirical force-field, showing that FP-LogMFD is a
promising method to calculate free energy without empirical force-fields.
