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<p>Dear all,</p>
<p><br>
</p>
<p>I am using thermo_pw in order to calculate the elastic properties as well as the Debye temperature of a series of systems.</p>
<p>For the majority of the calculations I get approximate Debye temperatures and Debye temperatures that differ by 1 K. However for some of the systems, such difference is significant (up to
<span>53 K for example</span>). Would it be possible to give me any hint about the reasons, this could happen. I am thinking if an increase of K-points leads to better results.</p>
<p><br>
</p>
<p>In addition, for only one of the systems that I am studying the approximate Debye temperature is not available, since according to the output t<span>he system is unstable for shear deformations. Is there any way to improve that, too?</span></p>
<p><span><br>
</span></p>
<p><span>Below I attach the main part of the inputs with the parts of the outputs that describe the elastic properties and Debye temperatures.</span></p>
<p><span><br>
</span></p>
<p><span><br>
</span></p>
<p><span>***********************************************************<br>
</span></p>
<p><span></p>
<div>Input:<br>
</div>
<div><br>
</div>
<div>&CONTROL<br>
calculation = "scf"<br>
! wf_collect = .true.<br>
title = 'scf',<br>
prefix = 'scf',<br>
restart_mode = 'from_scratch',<br>
pseudo_dir = '/PP/'<br>
outdir = './'<br>
nstep = 1000,<br>
tstress = .true.<br>
tprnfor = .true.<br>
/<br>
<br>
<br>
&SYSTEM<br>
ibrav = 14,<br>
nat = 146<br>
ntyp = 5,<br>
ecutwfc = 40 ,<br>
ecutrho = 280 ,<br>
celldm(1) = 34.24774975539434046984<br>
celldm(2) = 0.49825775128247714384<br>
celldm(3) = 1.35163407203943248213<br>
celldm(4) = 0.0<br>
celldm(5) = 0.0<br>
celldm(6) = -0.42<br>
/<br>
<br>
&ELECTRONS<br>
!electron_maxstep = 500,<br>
conv_thr = 1.d-8<br>
diagonalization = 'cg'<br>
/<br>
<br>
&IONS<br>
/<br>
<br>
&CELL<br>
/<br>
<br>
K_POINTS automatic<br>
2 2 1 1 1 1<br>
<br>
ATOMIC_SPECIES<br>
Pb 207.2 Pb.pbe-dn-rrkjus_psl.0.2.2.UPF<br>
I 126.904 I.pbe-n-rrkjus_psl.0.2.UPF<br>
C 12.0107 C.pbe-rrkjus.UPF<br>
N 14.0067 N.pbe-rrkjus.UPF<br>
H 1.00784 H.pbe-rrkjus.UPF<br>
<br>
</div>
<div>ATOMIC_POSITIONS (crystal)<br>
Pb 0.992789319 0.992744559 0.978309809<br>
Pb 0.991367642 0.989878647 0.146751474<br>
Pb 0.506306111 0.007712595 0.976472657<br>
Pb 0.504988223 0.004566493 0.144514039<br>
<div>
<div>
<div>....<br>
</div>
....<br>
</div>
....<br>
</div>
<br>
</div>
Output:<br>
</span>
<p></p>
<p><span></p>
<div> Voigt approximation:<br>
Bulk modulus B = 57.08571 kbar<br>
Young modulus E = 62.26770 kbar<br>
Shear modulus G = 23.61838 kbar<br>
Poisson Ratio n = 0.31820<br>
<br>
Reuss approximation:<br>
Bulk modulus B = 82.98611 kbar<br>
Young modulus E = 11.01452 kbar<br>
Shear modulus G = 3.72646 kbar<br>
Poisson Ratio n = 0.47788<br>
<br>
Voigt-Reuss-Hill average of the two approximations:<br>
Bulk modulus B = 70.03591 kbar<br>
Young modulus E = 36.64111 kbar<br>
Shear modulus G = 13.67242 kbar<br>
Poisson Ratio n = 0.33996<br>
<br>
Voigt-Reuss-Hill average; sound velocities:<br>
<br>
Compressional V_P = 1594.022 m/s<br>
Bulk V_B = 1419.902 m/s<br>
Shear V_G = 627.366 m/s<br>
<br>
The approximate Debye temperature is 76.616 K<br>
<br>
----------------------------------------<br>
<br>
Average Debye sound velocity = 229.337 m/s<br>
<br>
Debye temperature = 23.377 K</div>
<div><br>
</div>
<div>********************************************************************<br>
</div>
<div>Input:</div>
<div><br>
<div>&CONTROL<br>
calculation = "scf"<br>
! wf_collect = .true.<br>
title = 'scf for gap',<br>
prefix = 'scf',<br>
restart_mode = 'from_scratch',<br>
pseudo_dir = '/home/boziki/PP-new/PP/'<br>
outdir = './'<br>
nstep = 1000,<br>
tstress = .true.<br>
tprnfor = .true.<br>
/<br>
<br>
<br>
&SYSTEM<br>
ibrav = 14,<br>
nat = 144<br>
ntyp = 5,<br>
ecutwfc = 40 ,<br>
ecutrho = 280 ,<br>
celldm(1) = 34.59613963864875075156<br>
celldm(2) = 0.49999972688773829727<br>
celldm(3) = 1.33737830800399180881<br>
celldm(4) = 0.0<br>
celldm(5) = 0.0<br>
celldm(6) = -0.45<br>
/<br>
<br>
&ELECTRONS<br>
!electron_maxstep = 500,<br>
conv_thr = 1.d-8<br>
diagonalization = 'cg'<br>
/<br>
<br>
&IONS<br>
/<br>
<br>
&CELL<br>
/<br>
<br>
K_POINTS automatic<br>
2 2 1 1 1 1<br>
<br>
ATOMIC_SPECIES<br>
Pb 1 Pb.pbe-dn-rrkjus_psl.0.2.2.UPF<br>
I 1 I.pbe-n-rrkjus_psl.0.2.UPF<br>
C 1 C.pbe-rrkjus.UPF<br>
N 1 N.pbe-rrkjus.UPF<br>
H 1 H.pbe-rrkjus.UPF<br>
<br>
ATOMIC_POSITIONS (crystal)<br>
Pb 0.000285166 0.999427499 0.984407789<br>
Pb 0.999692114 0.000611651 0.151070638<br>
Pb 0.500287344 0.999428351 0.984408394<br>
...<br>
</div>
...<br>
</div>
...</span>
<p></p>
<p><span><br>
</span></p>
<p><span>Output:</span></p>
<p><span></p>
<div> Voigt approximation:<br>
Bulk modulus B = 79.06975 kbar<br>
Young modulus E = 61.02940 kbar<br>
Shear modulus G = 22.25142 kbar<br>
Poisson Ratio n = 0.37136<br>
<br>
Reuss approximation:<br>
Bulk modulus B = 91.94692 kbar<br>
Young modulus E = -1202.99533 kbar<br>
Shear modulus G = -163.42392 kbar<br>
Poisson Ratio n = 2.68060<br>
<br>
Voigt-Reuss-Hill average of the two approximations:<br>
Bulk modulus B = 85.50834 kbar<br>
Young modulus E = -570.98297 kbar<br>
Shear modulus G = -70.58625 kbar<br>
Poisson Ratio n = 3.04458<br>
<br>
Voigt-Reuss-Hill average; sound velocities:<br>
<br>
The system is unstable for compressional deformations<br>
Bulk V_B = 11446.859 m/s<br>
The system is unstable for shear deformations<br>
<br>
The approximate Debye temperature not available<br>
<br>
----------------------------------------<br>
<br>
Average Debye sound velocity = 1679.234 m/s<br>
<br>
Debye temperature = 169.977 K<br>
<br>
</div>
</span>
<p></p>
<p><span><br>
</span></p>
<p><span><span>Thank you very much in advance for your time.</span><br>
</span></p>
<p><span><br>
</span></p>
<p><span>Sincerely yours</span></p>
<p><span><br>
</span></p>
<p><span>Ariadni Boziki</span></p>
<p><span>EPFL<br>
</span></p>
<p><span></span><br>
</p>
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