[Pw_forum] relaxation of even-layer slab

[Stefano Baroni]

Dear Lucky:

the non-symmetric part of the relaxation is very small and possibly  
not very meaningful. Nevertheless, I agree that if reflection were an  
exact symmetry of your system, this asymmetry should vanish. One  
possible explanation could be that reflection symmetry is (slightly)  
violated by your numerical setup, e.g. the real-space fft grid could  
be not symmetryc.

Stefano

On Oct 11, 2006, at 3:14 AM, lucky8121 wrote:

> Dear users,
>
> I am a new user of PWSCF. I am doing the structure relaxation of  
> metal slabs.
> The relaxations (interlayer spacings) on the two sides of the odd- 
> layer slab are symmetric. However, I met problem with the  
> relaxation of even-layer slabs.
>
> The initial positions of the Cu(111) slab were:
> Cu       0.000000000   0.577350269190  -1.224744871392
> Cu       0.000000000   0.000000000000  -0.408248290464
> Cu       0.500000000   0.288675134595   0.408248290464
> Cu       0.000000000   0.577350269190   1.224744871392
>
> After relaxation (forc_conv_thr = 4.0D-4), the final positions are:
> Cu       0.000000000   0.577350269  -1.207031882
> Cu       0.000000000   0.000000000  -0.404842681
> Cu       0.500000000   0.288675135   0.404671325
> Cu       0.000000000   0.577350269   1.207203237
>
> As you can see, the relaxations on the two sides of the slab are  
> different. The same case occured whether I set "nosym" as ".true."  
> or ".false.". This is strange. I wonder whether someone else has  
> met the same problem and how he or she solved it. Thanks.
>
> By the way, I have used a vacuum of 12.7 angstrom.
>
> Best regards
>
> lucky
> lucky8121 at sohu.com
> 2006-10-11
>
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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