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<p>Dear Prof. Dal Corso.</p>
<p><br>
</p>
<p>I would like to thank you for your reply.</p>
<p><br>
</p>
<p>Sincerely yours,</p>
<p><br>
</p>
<p>Ariadni Boziki</p>
<p>EPFL<br>
</p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Thermo_pw-forum <thermo_pw-forum-bounces@lists.quantum-espresso.org> on behalf of Andrea Dal Corso <dalcorso@sissa.it><br>
<b>Sent:</b> 02 October 2020 11:54:47<br>
<b>To:</b> thermo_pw-forum@lists.quantum-espresso.org<br>
<b>Subject:</b> Re: [Thermo_pw-forum] Significant difference between the approximate Debye temperature and Debye temperature</font>
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<div class="PlainText">The approximate debye temperature is calculated as explained in<br>
<br>
Comp. Phys. Comm. 158, 57 (2004)<br>
<br>
and as written is approximated, but does not require the calculation of<br>
all elastic constants. It is shown only to gauge the approximation.<br>
<br>
Andrea<br>
<br>
<br>
On Fri, 2020-10-02 at 09:45 +0000, Boziki Ariadni wrote:<br>
> Dear all,<br>
> <br>
> <br>
> I am using thermo_pw in order to calculate the elastic properties as<br>
> well as the Debye temperature of a series of systems.<br>
> <br>
> For the majority of the calculations I get approximate Debye<br>
> temperatures and Debye temperatures that differ by 1 K. However for<br>
> some of the systems, such difference is significant (up to 53 K for<br>
> example). Would it be possible to give me any hint about the reasons,<br>
> this could happen. I am thinking if an increase of K-points leads to<br>
> better results.<br>
> <br>
> <br>
> In addition, for only one of the systems that I am studying the<br>
> approximate Debye temperature is not available, since according to<br>
> the output the system is unstable for shear deformations. Is there<br>
> any way to improve that, too?<br>
> <br>
> <br>
> Below I attach the main part of the inputs with the parts of the<br>
> outputs that describe the elastic properties and Debye temperatures.<br>
> <br>
> <br>
> <br>
> ***********************************************************<br>
> <br>
> Input:<br>
> <br>
> &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>
> 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>
> ....<br>
> ....<br>
> ....<br>
> <br>
> Output:<br>
> <br>
> 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<br>
> <br>
> ********************************************************************<br>
> Input:<br>
> <br>
> &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>
> ...<br>
> ...<br>
> <br>
> <br>
> Output:<br>
> <br>
> 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>
> <br>
> <br>
> Thank you very much in advance for your time.<br>
> <br>
> <br>
> Sincerely yours<br>
> <br>
> <br>
> Ariadni Boziki<br>
> <br>
> EPFL<br>
> <br>
> _______________________________________________<br>
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-- <br>
Andrea Dal Corso Tel. 0039-040-3787428<br>
SISSA, Via Bonomea 265 Fax. 0039-040-3787249<br>
I-34136 Trieste (Italy) e-mail: dalcorso@sissa.it<br>
<br>
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