[Pw_forum] A method on defining a based-centered monoclinic cell

[yinwei_li]

Sorry, everyone, MS is Materials Studio modeling.

 In fact, I found many users, as well as me, have problems on the input defining a based-centered monoclinic cell. For example, a c2m structure with 
a=11.692, b=2.159, c=3.463, beta=103.7, 
A  (0.152   0    0.373 )
B  (0.054    0.5    0.976) 
B  (0.745    0.5    0.889)
B  (0.946    0.5    0.388)
As described in the documentation, the input information is:
  ibrav=13,
  celldm(1)=22.09468665493776184528,
  celldm(2)=0.18465617516250427642,
  celldm(3)=0.29618542593226137529,
  celldm(4)=-0.236838146065618621,
  nat=8
  ntyp= 2,
...
...
ATOMIC_POSITIONS {crystal}
A   0.15200   0.15200   0.37300
A   0.84800   0.84800   0.62700
B    0.55400   0.55400   0.97600
B    0.24500   0.24500  -0.11100
B     0.44600   0.44600   0.38800
B     0.44600   0.44600   0.02400
B     0.75500   0.75500   0.11100
B     0.55400   0.55400   0.61200

....
However, this will give us a different structure with that in Materials Studio (MS). I know there is something 
wrong in my input, because the atomic positions I input are directly obtained from the Materials Studio (MS).
Unfortunately, the transformation matrix from the unit cell to the primitive cell is different between the MS 
and PWSCF, therefore, my input form is not accordance with the PWSCF, but I do not know how to change 
my input. However, If I change the defining form in the PWSCF to the one used in MS, with my input I will 
get a correct structure.  
 If some one could get a correct structure of the above parameters with the defining form in the PWSCF, please show me the input file.


Thanks!


2009-03-09 



 ***************************************
Yinwei Li （李印威）
PHD
State Key Lab of Superhard Materials, Jilin University
2699 Qianjin Str.
130012, Changchun
P. R. China
********************************************



发件人： Paolo Giannozzi 
发送时间： 2009-03-09  18:47:32 
收件人： PWSCF Forum 
抄送： 
主题： Re: [Pw_forum] A method on defining a based-centered monoclinic cell 
 
On Mar 7, 2009, at 4:14 , yinwei_li wrote:
>  In fact, we could  change the setting (ibrav=13) in the flib/ 
> latgen.f90 from
>  [...] to [...] which corresponding with the defining form in the MS.
MS = manuscript? Master of Science? Multiple Sclerosis?
>
> I have tested it and found this way of defining could give us a  
> right structure.
do you have any evidence that the current code produces an incorrect
structure, or that the documentation is incorrect? case ibrav=13 has  
been
corrected more than once and as far as I know it is both correct and
consistent with what the documentation says.
P.
---
Paolo Giannozzi, Democritos and University of Udine, Italy
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