[QE-users] Error in piezoelectric coefficients calculation (Berry phase)

[Paolo Giannozzi]

On 04/08/2023 16:17, ANAND JHA wrote:

> That's because nbnd is only used for calculation type BANDS

not really: the number of bands can be specified for any kind of 
calculation. It is typically, but not always, used for "bands" calculations.

The NaN (Not a Number) sgnals a floating-point error typically, overflow 
or division by zero. It appears only for nbnd > 54, though: for smaller 
values of nbnd it works for me. Not sure why

Paolo

> On Fri, 4 Aug 2023 at 19:43, Zimmi Singh <singh.60 at kgpian.iitkgp.ac.in> 
> wrote:
> 
>     Dear Users,
> 
>     I am attempting to calculate the piezoelectric coefficients of 2D
>     MoS2 using the Berry Phase method on a strained structure (0.5% in
>     the armchair direction).
> 
>     I faced two issues during the process.
> 
>     1) In the nscf calculations, I added the 'nbnd' tag in the input
>     file (nscf1.in <http://nscf1.in>). However, when examining the
>     output file (nscf1.out), the polarization value was displayed as NaN
>     (see below). I have attached the output file for your reference.
> 
>                                  VALUES OF POLARIZATION
>                                   ~~~~~~~~~~~~~~~~~~~~~~
> 
>              The calculation of phases done along the direction of vector 2
>              of the reciprocal lattice gives the following contribution to
>              the polarization vector (in different units, and being Omega
>              the volume of the unit cell):
> 
>                 P =         NaN  (mod  10.4913000)  (e/Omega).bohr
> 
>                 P =         NaN  (mod   0.0037363)  e/bohr^2
> 
>                 P =         NaN  (mod   0.2136113)  C/m^2
> 
>              The polarization direction is:  (-0.00000 , 1.00000 , 0.00000 )
> 
>     However, after removing the 'nbnd' tag in the nscf input file
>     (nscf.in <http://nscf.in>), I successfully obtained the polarization
>     values (see below), and also attached the output file (nscf.out)).
> 
>                                   VALUES OF POLARIZATION
>                                   ~~~~~~~~~~~~~~~~~~~~~~
> 
>              The calculation of phases done along the direction of vector 2
>              of the reciprocal lattice gives the following contribution to
>              the polarization vector (in different units, and being Omega
>              the volume of the unit cell):
> 
>                 P =  14.0341794  (mod  10.4913000)  (e/Omega).bohr
> 
>                 P =   0.0049981  (mod   0.0037363)  e/bohr^2
> 
>                 P =   0.2857471  (mod   0.2136113)  C/m^2
> 
>              The polarization direction is:  (-0.00000 , 1.00000 , 0.00000 )
> 
> 
>     2) At a strain of 0.5% in the armchair direction, the calculated
>     polarization vector is P = 0.2857471 C/m². To convert it to C/m, I
>     multiplied it by the armchair lattice parameter (10.5 angstroms) and
>     obtained the piezoelectric coefficient e22 = 60006.89 pC/m. However,
>     the published value for e22 is 362 pC/m (10.1021/acsnano.5b03394).
> 
>     I have scavenged through the mailing list but found no tutorial on
>     this topic.
> 
>     -- 
>     Best Regards
>     Zimmi Singh
>     /Ph.D. Candidate/
>     /Department of Metallurgical and Materials Engineering
>     Indian Institute of Technology, Kharagpur
>     Kharagpur, India/
>     /Mob No. 9935804727/
> 
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> 
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216