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

Tone Kokalj tone.kokalj at ijs.si
Mon Mar 30 23:45:26 CEST 2009

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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