[Pw_forum] CP for all systems

[Paul Tangney]

Hi Kostya and others,

 >I am proposing to restart CP with finite ionic velocities and MOVING
 >orbitals. This is achieved by doing a couple of BO (CG) steps for
 >moving ions, with the fully converged wavefunctions for the last 2
 >steps saved. This way CP will be restarted from the BO wavefunctions
 >which were moving with the ions and thus contain the full drag effect
 >(and only the drag effect!).
 >
 > I think this is identical to restarting CP with both ionic and
 >wavefunction velocities set to zero, only now they can be finite.


This is a very good idea!






I have a further suggestion for developers:

How about providing a means of rescaling the masses of the
ions in the code, as Sandro Scandolo and I showed was necessary
for the correct calculation of temperature, thermal pressure,
  and dynamical properties ?

A large part of the dragging effect is a renormalization of
the ionic masses by an amount dM.  That means that
temperature should be calculated as 3(N-1)kT = \sum (M+dM) v^2

A way to significantly improve dynamical properties and
calculate the temperature more correctly is to evolve the ions using
a mass of M-dM  (i.e. acceleration = F/(M-dM) ), and then to calculate
temperature with a mass of M.
(dM can be calculated by minimizing errors in Car-Parrinello
forces w.r.t. ground state forces....this could also be facilitated
in the code.)

It would be great if the code allowed you to input dM and have
it do the rescaling, the calculation of temperature both with
and without mass corrections (because away from the strongly-ionic
limit the definition of temperature is less clear), and the
calculation of the fictitious kinetic energy minus the
dragging contribution.

I used to have all this implemented in FPMD, but somehow it never
made its way into the official version.

Regards,

Paul


-- 
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
Dr. Paul Tangney
Theory of Nanostructured Materials Facility
The Molecular Foundry
Lawrence Berkeley National Lab.         E-mail: PTTangney at lbl.gov
1 Cyclotron Road, Bldg 66                  Phone: (510) 642-2635
Berkeley, CA 94720                         Fax :  (510) 643-9345
ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo