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

[vega lew]

Dear friends,

Thank you for you  time for reading and answering my questions.

I realized that the ensemble is much more important than one snap of the
whole run, resembling the classical MD to some extent.

I used to ask "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."

I didn't mean the same coordinates of the final systems. I wonder if the
different methods with same input coordinates will give us the same
conclusion. For example, By relax calculation by pw.x water disociative
adsorption is extremely favorable at certain metal surface with a minute
barrier of ~0.20 eV given by NEB method. But before the calculation we
didn't know this. Suppose we know nothing about it before the ab initio MD
calcualtions. We only take ab initio MD, and we put a integrated water
molecule at certain site on the surface. and then we perform MD calculations
of different method, such as CPMD, cp.x, pw.x(calcualtion='md'). I wonder
whether the dissociative state could be acheived on the surface at very low
temparature (such as 100K or below) via all the MD calculations mentioned
above?

>From your answers, I see cp.x and CPMD of IBM CORP. is using 'Car-Parrinello
Molecular Dynamics', while the 'md' calculation in pw.x performs
born-oppenheimer MD. Paolo just told us that the born-oppenheimer MD only
perform MD at ground state. Does CPMD or cp.x perform the MD calculation at
ground state or exited state?


thank you very much for you time

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
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Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
Jiangsu, China
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