[Pw_forum] what's the difference between 'md' in pw.x and cp.x

[Axel Kohlmeyer]

On Mon, Jun 22, 2009 at 4:39 AM, vega lew<quantumdft at gmail.com> wrote:
> Dear all,
>
> I want to perform ab initio molecular dynamics calculation via Q-E. I found
> both cp.x and pw.x could undertake this calculation.
> I wonder what's the difference between 'md' in pw.x and cp.x, and if I could
> achieve the same final geometry for same systems (the coordinates of atoms,
> temparature, box dimensions and K-ponits etc. are exactly the same) by this
> two methods.

with MD you will never get the exact same end configuration out of two
trajectories
if there are the tiniest differences, let alone they are done with two
different codes
or slightly different methods. this doesn't matter, because the
individual geometry
doesn't matter, only the ensemble.

n.b.: cp.x only supports gamma point.

> Do you think both 'md' calculation in pw.x and 'cp' in cp.x could be regard
> as the 'Car-Parrinello Molecular Dynamics' calculation and do the almost the
> same thing as the 'CPMD' codes copyrighted jointly by IBM Corp.

cp.x and CPMD have the same origin. both codes can perform CP dynamics,
but also born-oppenheimer MD. however, both codes cater somewhat different
communities and thus are better suited for specific but different scenarios.
pw.x only does born-oppenheimer dynamics. for some systems, CP dynamics
can be much more efficient, but the CP method imposes limitations, that have
to be understood to do correct calculations.


cheers,
   axel.
> thank you for reading
>
> best,
>
> vega
> --
> ==================================================================================
> Vega Lew ( weijia liu)
> PH.D Candidate in Chemical Engineering
> State Key Laboratory of Materials-oriented Chemical Engineering
> College of Chemistry and Chemical Engineering
> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
> ******************************************************************************************************************
> Email: vegalew at gmail.com
> Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
> Jiangsu, China
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>
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-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
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