[Pw_forum] (2) about the logical parameter "use_masses" in IONS card

[Tone Kokalj]

On Mon, 2009-03-30 at 21:59 +0800, lfhuang wrote:
> Any original papers or good papers on the parameter "use_masses" ?

There is no paper on use_masses (as far as I know).
Normaly one does not need to use use_masses.

This parameter was added out of experience with some systems for the quick-min NEB minimization
(i.e. quick-min is a kind of damped dynamics). 

If some bond is much stiffer than the others then this bond will prevent using larger ds (=time step).
Say for example that you want to break C-H bond of adsorbed C2H2 molecule. The triple CC bond is 
much stiffer than the others, and in this case one may assign to C atom larger "fictitous" mass compared to other atoms.
For example you can assing to C a mass of, say, 1.5 and to H the mass of 1.0.

If use_masses aids in faster convergence in a given case, and what is the optional ratio 
between masses, have to be tested. It is difficult to tell it in advance.

Regards, Tone

-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

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