This package contains 2 fix commands, "fix qtb" and
"fix qbmsst" which involve quantum nuclear effects.

What is quantum nuclear effects (in molecular dynamics
simulation)?
        Quantum treatment of the vibrational modes will
        introduce zero point energy into the system, alter
        the energy power spectrum and bias the heat capacity
        from the classical limit. classical MD leaves out
        these effects completely and thus need to be corrected.

When should I consider quantum nuclear effects in
my simulation?
        (1) When you want to model systems at temperatures
        lower than their classical limits. This is especially
        important for materials with a large population of
        hydrogen atoms and thus higher classical limits.

        (2) In MD simulations when temperatures ramp up
        across (or starting from somewhere close to) the
        classical limits, tiny differences between the
        classical and quantum heat capacity can accumulate
        and cause the final state to deviate (could be as
        large as 30 %).

What command should I use regarding these two cases?
        (1) "fix qtb" provides quantum nulcear correction
        through a colored thermostat and can be used with
        other time integration schemes like fix nve or
        fix nph. In this case, you tell "fix qtb" the temperature
        and the other time integration scheme either the
        pressure ("fix nph") or the volume ("fix nve").

        (2) "fix qbmsst" deals with shock MD simulations
        in which cases the temperature may increase a lot.
        It enables quantum nuclear correction of a multi-scale
        shock technique simulation by coupling the quantum
        thermal bath with the shocked system. It is an independent
        command from "fix msst" and does not assume that
        the SHOCK package has been installed.

        See the doc page for the fix qtb and fix qbmsst
        command for detailed usage instructions.

Where can I find examples of these two commands?
        There are example scripts for using this package in
        examples/PACKAGES/qtb, including one "fix qtb" and one
        "fix qbmsst" example for each of alpha quartz and
        methane. Running the alpha quartz example requires
        installation of the kspace package while the methane
        example requires the REAX package for the force field.

Authors Information and Contact
        The person who created this package is Yuan Shen
        (sy0302 at stanford.edu) at Stanford University.
        Contact him directly if you have questions.
