The ABINIT Users Mailing List ( CLOSED )

["Riad Shaltaf" <Riad.Shaltaf@uclouvain.be>]

Dear Tularam,

Within modern theory of polarization, the total polarization may only be
determined up to an integer multiple of the polarization quantum. So I
guess
that you need to subtract the value of polarization quantum or one of its
multiples from the the ABINIT result.

for more details: Neaton et al, PRB 71, 014113 (2005)

Riad

> Dear all,
>
> I am trying the spontaneous polarization of the III-V nitrides. Here is my
> input file for the GaN
> # Specific to calculation of Berry Phase.
>   berryopt -1
>   rfdir 1 1 1
> #Definition of the planewave basis set
>   ecut          100.0
>   ectusm  0.5
>   dilatmx 1.05
>   diemac  6.0
>
> #Specific to ground state calculation
>   iscf         5
>   nstep  60
>
> #Definition of the unit cell
> acell  6.026 6.026  9.798276
> angdeg 90 90 120
>
> #Definition of the atom types
> ntypat 2
> znucl 31 7
>
> #Definition of the atoms
> natom 4
> typat 1 1 2 2
> xred  0.0  0.0        0.0
>       2/3  1/3        1/2
>       0    0  0.377
>       2/3 1/3 0.877
>
> #Gives the number of band, explicitely (do not take the default)
> nband  18             # For an insulator (if described correctly as an
> insulator
>
> #Exchange-correlation functional
> ixc 1
>
> #Definition of the k-point grid
> ngkpt 4 4 8
> nshiftk 1
> shiftk 0 0 .5
> kptopt          3
> toldfe          1.0d-12
> nbdbuf 0
>
> I used hgh pseudopotential, hence used high cutoff. But my result for the
> zz
> part of polarization is as follow
>  Computing the polarization (Berry phase) for reciprocal vector:
>   0.00000  0.00000  0.12500 (in reduced coordinates)
>   0.00000  0.00000  0.01276 (in cartesian coordinates - atomic units)
>  Number of strings:    16
>  Number of k points in string:          8
>
>  Summary of the results
>  Electronic Berry phase     9.622896788E-01
>           Ionic phase     7.700000000E-01
>           Total phase     1.732289679E+00
>     Remapping in [-1,1]    -2.677103212E-01
>
>          Polarization    -8.512874458E-03 (a.u. of charge)/bohr^2
>          Polarization    -4.870620906E-01 C/m^2
>
>
>  Polarization in cartesian coordinates (a.u.):
>  (the sum of the electronic and ionic Berry phase has been fold into [-1,
> 1])
>      Electronic:  0.399941195E-12  -0.113753605E-11   0.305996840E-01
>      Ionic:     0.318961478E-16  -0.868508257E-17   0.244850976E-01
>      Total:     0.399969197E-12  -0.113755148E-11  -0.851287446E-02
>
>  Polarization in cartesian coordinates (C/m^2):
>  (the sum of the electronic and ionic Berry phase has been fold into [-1,
> 1])
>      Electronic:  0.228825405E-10  -0.650838549E-10   0.175075365E+01
>      Ionic:     0.182493052E-14  -0.496914937E-15   0.140090904E+01
>      Total:     0.228841426E-10  -0.650847378E-10  -0.487062091E+00
>
> But the total zz polarization of-0.48 is more then a order of magnitude
> greater
> then reported p_zz of -0.029 reported in Phys. Rev B 56, R10024. I don't
> understand the differences as both of them are similar first principle
> calculation.   So I am wondering, if I am wrong ?. I played with the fhi
> psedudopotential and obvious tests with the cutoff kpoints , Berryopt, but
> the
> result is same.
>
> I would appreciate if anyone help me how to calculate the spontaneous
> polarization correctly.
>
> Thanks in an advance.
>
> Tularam
>
-- 
Dr. Riad Shaltaf                   UCL/SE/FSA/MAPR/PCPM
Tel: +32 (0)10 47 36 30            Bâtiment Boltzmann, a+1
Fax: +32 (0)10 47 34 52            1 place Croix du Sud
Mel: riad.shaltaf@uclouvain.be     1348 Louvain-la-Neuve (Belgique)