[Pw_forum] Atom Mass in vc-relax or relaxation

Paolo Giannozzi giannozz at nest.sns.it
Thu Sep 6 18:42:15 CEST 2007

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 Giannozzi, Democritos and University of Udine, Italy

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