<div dir="ltr">Hello <span style="font-family:arial,sans-serif;font-size:13px">Shahrbano,</span><div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div><div><div><span style="font-size:13px;font-family:arial,sans-serif">I was able to compute the Effective charge of GaN using the structure files provided by Dr. Rubel. This is how it looks,</span></div><div><span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div><div style="font-size:13px;font-family:arial,sans-serif">>>> Z=(1.76267778062-1.7075251678616241)/0.02</div><div><span style="font-family:arial,sans-serif;font-size:13px">Z=2.7576306379187954</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">My computed effective charge seems to almost the same as computed by Dr. Rubel. </span></div>
</div><div><span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div><div><span style="font-family:arial,sans-serif;font-size:13px">I think you are using older versions of either BerryPI or Wien2Wannier or both. Please use the latest version of BerryPI (v1.0) </span><a href="https://github.com/spichardo/BerryPI" target="_blank">https://github.com/spichardo/BerryPI</a> and Wien2Wannier (v0.97) <a href="http://www.wien2k.at/reg_user/unsupported/wien2wannier/" target="_blank">http://www.wien2k.at/reg_user/unsupported/wien2wannier/</a>.</div>
<div><br></div><div>The older version of BerryPI (v0.1) had some problem in wrapping of phases which has been fixed in version 1.0. Also, the older versions of Wien2wannier was having an issue in identifying the complex calculation <span style="font-size:13px;font-family:arial,sans-serif">(see the post </span><a href="http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09119.html" style="font-size:13px;font-family:arial,sans-serif" target="_blank">http://www.mail-archive.com/<u></u>wien@zeus.theochem.tuwien.ac.<u></u>at/msg09119.html</a><span style="font-size:13px;font-family:arial,sans-serif">)</span></div>
<div><br></div><div>Regards</div><div>Sheikh</div>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Nov 4, 2013 at 5:13 PM, Oleg Rubel <span dir="ltr"><<a href="mailto:orubel@lakeheadu.ca" target="_blank">orubel@lakeheadu.ca</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Shahrbano,<br>
<br>
I was able to obtain the effective charge of Z(Ga) = 2.76<br>
<br>
Here is the approach:<br>
<br>
1) Take the structure files enclosed (I assume they are not different from yours).<br>
<br>
2) create directories 'lambda1' and 'lambda2'. In both cases I displace the Ga atom by +0.01 and -0.01 along z-axis. There is nothing specific about the choice of displacements. In fact 0.005 should work too. I encourage you to test the convergence and plot Z as a function of displacement. I do not recommend to go for displacements larger than 0.01<br>
<br>
3) initialize both using 'init_lapw -b -vxc 13 -ecut -6 -numk 230'<br>
<br>
4) rum wien2k 'run_lapw'<br>
<br>
5) run berrypi 'berrypi -p$(pwd) -k6:6:4'. You should obtain the output as shown below.<br>
<br>
6) Z = (1.7626777806241982 - 1.7075447765644145)/(0.01+0.<u></u>01) = 2.76<br>
(see Eq. 14 in <a href="http://www.tbrri.com/~orubel/publications/2013/Ahmed_CPC_184_2013.pdf" target="_blank">http://www.tbrri.com/~orubel/<u></u>publications/2013/Ahmed_CPC_<u></u>184_2013.pdf</a>)<br>
<br>
The result really close to Vanderbilt. Good sign :)<br>
<br>
In order to address the spontaneous polarization, we need two cases:<br>
(a) the initial reference structure and<br>
(b) your relaxed structure.<br>
The spontaneous polarization is the difference between them. Please, look in the literature what is used as a reference structure. The choice of structure (a) for GaN is not obvious to me. Once you determine that, I can help you to move on.<br>
<br>
<br>
Thank you<br>
Oleg<br>
<br>
<br>
<br>
++++++++++++++++++++++++++++++<u></u>+++++<br>
---PHASES/2*PI IN [0 to 2]RANGE---<br>
<br>
IONIC PHASE/(2*PI): [6.010209219198259e-08, 1.9999999400510458, 0.8898641300788697]<br>
<br>
ELECTRONIC PHASE/(2*PI): [2.000035665164408, -3.5664951224354753e-05, 0.87281365054532878]<br>
<br>
TOTAL PHASE/(2*PI): [3.572526650019725e-05, 1.9999642750998212, 1.7626777806241982]<br>
<br>
<br>
---POLARIZATION IN C/m^2 FOR [0 to 2] PHASE/2PI RANGE---<br>
<br>
IONIC POLARIZATION: [6.734131068339737e-08, 2.2408973201721545, 1.6229398446248238]<br>
<br>
ELECTRONIC POLARIZATION: [2.2409373483287527, -3.9960748009166113e-05, 1.5918430719045986]<br>
<br>
TOTAL POLARIZATION: [4.0028328181192241e-05, 2.2408573594241452, 3.2147829165294222]<br>
<br>
<br>
---PHASES/2*PI IN [-1 to +1]RANGE---<br>
<br>
IONIC PHASE/(2*PI): [6.010209219198259e-08, -5.994895424521474e-08, 0.8898641300788697]<br>
<br>
ELECTRONIC PHASE/(2*PI): [3.5665164408005268e-05, -3.5664951224312347e-05, 0.87281365054532878]<br>
<br>
TOTAL PHASE/(2*PI): [3.572526650019725e-05, -3.5724900178779606e-05, -0.23732221937580178]<br>
<br>
<br>
---POLARIZATION IN C/m^2 FOR [-1 to +1] PHASE/2PI RANGE---<br>
<br>
IONIC POLARIZATION: [6.734131068339736e-08, -6.716972747098987e-08, 1.6229398446248238]<br>
<br>
ELECTRONIC POLARIZATION: [3.9960986870508846e-05, -3.9960748009118604e-05, 1.5918430719045986]<br>
<br>
TOTAL POLARIZATION: [4.0028328181192241e-05, -4.0027917736838375e-05, -0.432829768973433]<br>
<br>
+++++++++++++++++++++++++<br>
---PHASES/2*PI IN [0 to 2]RANGE---<br>
<br>
IONIC PHASE/(2*PI): [6.010209219198259e-08, 1.9999999400510458, 0.6298641300758288]<br>
<br>
ELECTRONIC PHASE/(2*PI): [-2.9599378548340341e-05, 2.0000295996358957, 1.0776806464885857]<br>
<br>
TOTAL PHASE/(2*PI): [1.9999704607235438, 2.9539686940971421e-05, 1.7075447765644145]<br>
<br>
<br>
---POLARIZATION IN C/m^2 FOR [0 to 2] PHASE/2PI RANGE---<br>
<br>
IONIC POLARIZATION: [6.734131068339737e-08, 2.2408973201721545, 1.1487501955039068]<br>
<br>
ELECTRONIC POLARIZATION: [-3.3164585027959612e-05, 2.2409305522152549, 1.9654807985263416]<br>
<br>
TOTAL POLARIZATION: [2.2408642900981648, 3.3097703644459985e-05, 3.1142309940302484]<br>
<br>
<br>
---PHASES/2*PI IN [-1 to +1]RANGE---<br>
<br>
IONIC PHASE/(2*PI): [6.010209219198259e-08, -5.994895424521474e-08, 0.6298641300758288]<br>
<br>
ELECTRONIC PHASE/(2*PI): [-2.9599378548406108e-05, 2.9599635895660725e-05, -0.92231935351141425]<br>
<br>
TOTAL PHASE/(2*PI): [-2.9539276456214125e-05, 2.9539686940971421e-05, -0.2924552234355855]<br>
<br>
<br>
---POLARIZATION IN C/m^2 FOR [-1 to +1] PHASE/2PI RANGE---<br>
<br>
IONIC POLARIZATION: [6.734131068339736e-08, -6.716972747098987e-08, 1.1487501955039066]<br>
<br>
ELECTRONIC POLARIZATION: [-3.3164585028033304e-05, 3.3164873372428553e-05, -1.6821318869765136]<br>
<br>
TOTAL POLARIZATION: [-3.3097243717349902e-05, 3.3097703644459985e-05, -0.53338169147260672]<br>
++++++++++++++++++++++++++++++<u></u>+++++<br>
<br>
On 04/11/2013 3:35 AM, Shahrbano Raheme wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear Prof Oleg Rubel,______<br>
I went trough tutorials 1 and 2 of the BerryPI, and could reproduce the<br>
results without any problems.<br>
But, now I would like to calculate the spontaneous polarization for the<br>
GaN __<br>
structure. For sure, GaN.struct is pasted at the end of this e-mail. I<br>
have done these steps;____<br>
1.I relaxed the system____<br>
2.init_lapw____<br>
3.run_lapw____<br>
4.Run BerryPI using python____<br>
__ __<br>
I found the following values:____<br>
·____________________________<u></u>______________________________<u></u>Total phase<br>
in z directionbetween [0 - 2] range ..... 0.4468____<br>
·Total polarization in z direction between [0 - 2] range......0.8204____<br>
·Total phase in z direction between [-1 - +1] range...... 0.4498____<br>
·Total polarization in z direction between [-1 - +1] range.....__<br>
______0.8204____<br>
__ __<br>
But the value of polarization in “arXiv:1201.4294v3 [cond-mat.mar-sci] 6<br>
Aug 2012 “ is__ reported to be ______– 0.02.____<br>
So, would you help me, how I can improve my result.____<br>
My another question is about Born effective charge. Idisplaced the<br>
second Ga atom along the z-axisin relaxed struct file.†ATOM-2:<br>
X=0.66666667 Y=0.33333333 Z=0.50004893†____<br>
__ ____ __<br>
Displacement____<br>
<br>
Total phase in z directionbetween [0 - 2] range____<br>
<br>
Total polarization in z direction between [0 - 2] range____<br>
<br>
Total phase in z direction between [-1 - +1] range____<br>
<br>
Total polarization in z direction between [-1 - +1] range____<br>
+0.01____<br>
<br>
0.4122____<br>
<br>
0.7518____<br>
<br>
0.4122____<br>
<br>
0.7518____<br>
-0.01____<br>
<br>
0.0523____<br>
<br>
0.0955____<br>
<br>
0.0523____<br>
<br>
0.0955____<br>
<br>
__ __<br>
Iobtainedthese values according the readme of tuturial2. When I<br>
calculate the born effective charge, my result is far from -2.72 which<br>
is reported in “D. Vanderbilt, J. Phys. Chem. Solids 61 (2000) 147.†____<br>
Please help me to improve my results.____<br>
<br>
Do the results depend on the displacement? If they do, which<br>
displacement should we select? In the tutorials of BerryPI, 0.01 and<br>
-0.01 are selected for the displacements? But, it is not clear for me<br>
why these displacements are selected? For example, we did a test by<br>
-0.002 and 0.002 displacements and found completely different results.<br>
Should we try by changing the displacements to reproduce the<br>
experimental results.<br>
<br>
GaN<br>
H4186_P63mc<br>
RELA<br>
6.0206706.0206709.800124 90.000000 90.000000 60.000000<br>
ATOM-1: X=0.00000000 Y=0.00000000 Z=0.00004872<br>
MULT= 1ISPLIT= 4<br>
Ga1NPT=781R0=0.00005000 RMT=1.9600Z:<a href="tel:31.00000" value="+13100000" target="_blank">31.00000</a><br>
LOCAL ROT MATRIX:1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
0.0000000 0.0000000 1.0000000<br>
ATOM-2: X=0.66666667 Y=0.33333333 Z=0.50004893<br>
MULT= 1ISPLIT= 4<br>
Ga2NPT=781R0=0.00005000 RMT=1.9600Z:<a href="tel:31.00000" value="+13100000" target="_blank">31.00000</a><br>
LOCAL ROT MATRIX:1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
0.0000000 0.0000000 1.0000000<br>
ATOM-3: X=0.00000000 Y=0.00000000 Z=0.37603484<br>
MULT= 1ISPLIT= 4<br>
N 1NPT=781R0=0.00010000 RMT=1.6900Z:7.00000<br>
LOCAL ROT MATRIX:1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
0.0000000 0.0000000 1.0000000<br>
ATOM-4: X=0.66666667 Y=0.33333333 Z=0.87603488<br>
MULT= 1ISPLIT= 4<br>
N 2NPT=781R0=0.00010000 RMT=1.6900Z:7.00000<br>
LOCAL ROT MATRIX:1.0000000 0.0000000 0.0000000<br>
0.0000000 1.0000000 0.0000000<br>
0.0000000 0.0000000 1.0000000<br>
6NUMBER OF SYMMETRY OPERATIONS<br>
<br>
Your comments will be appreciated.<br>
<br>
Best wishes,<br>
SH. Rahimi<br>
</blockquote>
<br>
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<br></blockquote></div><br></div>