  Biased sampling methods such as the Temperature Accelerated Sliced Sampling
(TASS), which can explore high dimensional collective variable (CV) space, is
of great interest in free energy calculations. Such methods can efficiently
sample configurational space even when a large number of CVs for biasing are
used while many conventional methods are limited to two or three CVs. In this
paper, we propose a modification to the TASS method, called Parallel Bias TASS
or PBTASS, wherein a multidimensional parallel metadynamics bias is
incorporated on a selected set of CVs. The corresponding time-dependent
reweighting equations are derived, and the method is benchmarked. In
particular, we compare the accuracy and efficiency of PBTASS with various
methods viz. standard TASS, Temperature Accelerated Molecular
Dynamics/driven-Adiabatic Free Energy Dynamics, and Parallel Bias Metadynamics.
We demonstrate the capability of the PBTASS method by reconstructing the
eight-dimensional free energy surface of alanine pentapeptide in vacuo from a
25 ns long trajectory. Free energy barriers and free energies of high energy
saddle points on the high dimensional free energy landscape of this system are
reported.
