[Pw_forum] Zr supercell

[Krishnendu Mukherjee]

Dear expert,

 This is in response to the question why do we want to use a Zr supercell.
We are interested in calculating the elastic constants of Zr alloys (for
example Zr containing 1 wt% Nb). We found a paper titled, "Mechanical
properties of zirconium alloys and zirconium hydrides predicted from
density functional perturbation theory". In that paper the authors
constructed a Zr53Nb supercell with 53 Zr atoms and 1 Nb atom to do the
calculations. As a first step we want to replicate the results. To begin,
we just try to make a Zr supercell. When we are successful in creation of
Zr supercell and able to predict the elastic constants of Zr with the
supercell properly we will replace a Zr atom in that supercell with Nb to
get the elastic constants of the alloy.

 Now my question is,  is it possible to calculate the elastic properties of
Zirconium alloy without constructing a supercell, i.e., through an unit
cell? In that can you please let us know what will be the input parameters
to construct such an unit cell?

 Now in case, if construction of supercell is unavoidable can you please
guide us what are the input to construct the supercell. I guess we have to
input the space group (194, P 63/m m c in this case). I guess the other
input is the basis atom positions which is 0,0,0 and 2/3, 1/3, 1/2. Is
there any other input for constructing a supercell. I will use the program
VESTA for creating a supercell.

 I found some previous discussions in the pwscf forum about the space group
194. There I saw ibarv=4 was used, with some other necessary inputs,
e.g., use_all_frac = .true.. But in that case the input for the
ATOMIC_POSITIONS are to be given in crystal_sg. But I do not know how to
get the crystal_sg output from VESTA.

 I will be grateful to you if you can kindly guide us regarding these
matters.

Thanking you,
Yours sincerely,
krish


-- 
Dr. Krishnendu Mukherjee,

Principal Scientist,
CSIR-NML,
Jamshedpur.
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