[Pw_forum] Atom Mass in vc-relax or relaxation

Cesar R.S. da Silva cesards at msi.umn.edu
Thu Sep 6 20:57:38 CEST 2007

Dear Yukihiro,

The answer to your question "can I change atomic mass arbitrary instead of
true atom mass?" is YES! Fastest relaxation is obtained if you set all
atomic masses to the mass average.

Be aware that cell mass is not the sum of the atomic masses. This is the
default and is a terrible choice. This is the most likely reason you have
not noticed andy change in the cell. My suggestion is to start with
wmass==2*10**(-3) and dt=80 and see what happens.



> Message: 8
> Date: Fri, 07 Sep 2007 00:50:48 +0900
> From: Yukihiro Okuno <okunoyukihiro2000 at yahoo.co.jp>
> Subject: [Pw_forum] Atom Mass in vc-relax or relaxation
> To: pw_forum at pwscf.org
> Message-ID: <200709061550.AA00338 at Einstein.yahoo.co.jp>
> Content-Type: text/plain; charset=us-ascii
> Dear PW Users.
> I want to optimize the lattice parameter and internal atomic position, so
> I choose
> vc-relax calculation.
> In the relaxation , can I change atomic mass arbitrary instead of true
> atom mass?
> In the test calculation, I had changed the mass of the system and get
> almost same
> lattice parameter and atomic internal position.
> Does not relative relation of crystal coordinate of atoms depend on their
> mass ?
> 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?
> Sincerely,
> Yukihiro Okuno.
> ----
> Yukihiro Okuno  okunoyukihiro2000 at yahoo.co.jp

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