[Pw_forum] PWscf can not find out symmetry operations!!!

[Stefano Baroni]

Dear Niu Ying Li,

this very same question has been discussed many times in this forum,  
the last of which only a few days ago. Would you be so kind as to  
browse the archive of the mailing list and revert us after finding  
and reading the some of the relevant posts, in case the situation is  
not yet clear to you?

Many thanks for your interest in Quantum ESPRESSO

Stefano Baroni

On Aug 29, 2006, at 6:16 PM, 英利 牛 wrote:

> Dear all,
>   I am calculate properties of diamond
> surface(001),the lattice parameters of the slab is :
> 2.5221A,5.0442A,16.0253A,90,90,90
> after atoms relax ,the atom positions(crystal) are:
> C     0.24978  -0.11238   0.21129
>
> C     0.24980   0.60988   0.21129
>
> C     0.74978  -0.01422   0.17583
>
> C     0.74980   0.51175   0.17582
>
> C     0.74981   0.24879   0.13029
>
> C     0.74981   0.74881   0.11624
>
> C     0.24982   0.24883   0.07780
>
> C     0.24982   0.74885   0.07061
>
> C     0.24984  -0.00014   0.02461
>
> C     0.24984   0.49787   0.02461
>
> C     0.74985  -0.00211  -0.02461
>
> C     0.74986   0.49988  -0.02461
>
> C     0.74987   0.24889  -0.07061
>
> C     0.74987   0.74888  -0.07780
>
> C     0.24987   0.24889  -0.11624
>
> C     0.24988   0.74888  -0.13029
>
> C     0.24990   0.01186  -0.17582
>
> C     0.24987   0.48589  -0.17583
>
> C     0.74990   0.11000  -0.21129
>
> C     0.74987   0.38773  -0.21129
>
>
> but PWscf can not find any symmetry operations of the
> system.
> I setup the struct and use Material Studio find 8
> space group operations include inversion! The
> tolerance is 0.01A.
>
> Then I read PW manual:
>
> the number of significant figures in the atomic
> positions is not large enough. In file PW/eqvect.f90,
> the variable accep is used to decide whether a
> rotation is a symmetry operation. Its current value
> (10-5 ) is quite strict: a rotated atom must coincide
> with another atom to 5 significant digits. You may
> change the value of accep and recompile.
>
> I change accep from 1.0d-5 to 1.0d-2 then to 1.0d-1
> ,but PWscf still find no symmetry.
>
> What should I do?
> Why pwscf choose 1.0d-5,so strict?
>
>
> 	
>
> 	
> 		
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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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