[Pw_forum] metallic BP?

[giacsport at libero.it]

Hi Paolo,
               thanks for the reply and escuse me for the previous lacking 
description of the problem.
I have a question that you for sure will be able to reply.

It seems that I was able to fix the problem. I will try to explain.

In my first attempt I was using the Primitive Cell of BP consisting of two 
atoms. It is a rhombohedral cell, a=b=c=6.06 Bohr   and alpha=beta=gamma=60 deg 
(ibrav=  4, celldm(1) =6.06, celldm(3)=1)

 B  0.0000  0.0000  0.0000
 P  1.1373  1.1373  1.1373
-2  0.0000  2.2745  2.2745
-2  2.2745  0.0000  2.2745
-2  2.2745  2.2745  0.0000

(first 2 lines atomic coordinates, last three the lattice vectors)
reported in the Supplementary Materials of THE JOURNAL OF CHEMICAL PHYSICS 
123, 174101 (2005)


It gave as result that strange bandgap I reported before (formally no gap). 
espresso.4.1.3 (both serial and parallel)

Then I used exactly the same atomic position and configuration (2 atoms, 1 B 
and 1 P) but with the lattice parameters of the Conventional Cell (ibrav=  2, 
celldm(1) =8.575576536) and in this case I found perfect agreement (of course 
with some obvious DFT underestimation of the gap).

Thus, as far as I understand, if I have the Primitive Cell coordinates I have 
to use in any case the Conventional Cell lattice vectors.

Is it correct?
Thanks in advance and excuse me once more!

My very best,
Giacomo



----------------------------------
Giacomo GIORGI

Department of Chemical System Engineering,
School of Engineering, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Ja


>----Messaggio originale----
>Da: giannozz at democritos.it
>Data: 03/12/2011 11.04
>A: <giacsport at libero.it>, "PWSCF Forum"<pw_forum at pwscf.org>
>Ogg: Re: [Pw_forum] metallic BP?
>
>
>On Dec 3, 2011, at 9:39 , giacsport at libero.it wrote:
>
>> The structure is the experimental one I found from a previous paper
>> and it was optimized with Gaussian PBC
>
>are you sure? it yields very high forces and a very large stress.
>It also has just 2 symmetries.
>
>Reminder to everybody reporting problems:
>- if you use pseudopotentials from www.quantum-espresso.org,
>   please do not change the names of pseudopotential files
>- please always report the version of QE you are using
>
>P.
>---
>Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
>Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
>