[Pw_forum] Atom Mass in vc-relax or relaxation

[Paolo Giannozzi]

On Sep 6, 2007, at 17:50 , Yukihiro Okuno wrote:

> In the relaxation , can I change atomic mass arbitrary instead of  
> true atom mass?

you can

> Does not relative relation of crystal coordinate of atoms depend on  
> their mass ?

not necessarily; there are algorithms that make usage of atomic masses
for structural optimization, but most algorithms I know don't

> And if some atoms have heavy mass and does not move, and then they  
> cause the difficulties of conversence, is it one way to set same  
> masses for all atoms
> to improve the conversence?

it is: when damped dynamics is used to achieve structural relaxation,
this is a simple and effective way to "precondition" the dynamics, i.e.
to avoid having both "slow" and "fast" degrees of freedom, with wildly
different speed of approach to the minimum

Paolo
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Paolo Giannozzi, Democritos and University of Udine, Italy