[Thermo_pw-forum] Significant difference between the approximate Debye temperature and Debye temperature
Andrea Dal Corso
dalcorso at sissa.it
Fri Oct 2 11:54:47 CEST 2020
The approximate debye temperature is calculated as explained in
Comp. Phys. Comm. 158, 57 (2004)
and as written is approximated, but does not require the calculation of
all elastic constants. It is shown only to gauge the approximation.
Andrea
On Fri, 2020-10-02 at 09:45 +0000, Boziki Ariadni wrote:
> Dear all,
>
>
> I am using thermo_pw in order to calculate the elastic properties as
> well as the Debye temperature of a series of systems.
>
> 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 53 K for
> example). 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.
>
>
> In addition, for only one of the systems that I am studying the
> approximate Debye temperature is not available, since according to
> the output the system is unstable for shear deformations. Is there
> any way to improve that, too?
>
>
> Below I attach the main part of the inputs with the parts of the
> outputs that describe the elastic properties and Debye temperatures.
>
>
>
> ***********************************************************
>
> Input:
>
> &CONTROL
> calculation = "scf"
> ! wf_collect = .true.
> title = 'scf',
> prefix = 'scf',
> restart_mode = 'from_scratch',
> pseudo_dir = '/PP/'
> outdir = './'
> nstep = 1000,
> tstress = .true.
> tprnfor = .true.
> /
>
>
> &SYSTEM
> ibrav = 14,
> nat = 146
> ntyp = 5,
> ecutwfc = 40 ,
> ecutrho = 280 ,
> celldm(1) = 34.24774975539434046984
> celldm(2) = 0.49825775128247714384
> celldm(3) = 1.35163407203943248213
> celldm(4) = 0.0
> celldm(5) = 0.0
> celldm(6) = -0.42
> /
>
> &ELECTRONS
> !electron_maxstep = 500,
> conv_thr = 1.d-8
> diagonalization = 'cg'
> /
>
> &IONS
> /
>
> &CELL
> /
>
> K_POINTS automatic
> 2 2 1 1 1 1
>
> ATOMIC_SPECIES
> Pb 207.2 Pb.pbe-dn-rrkjus_psl.0.2.2.UPF
> I 126.904 I.pbe-n-rrkjus_psl.0.2.UPF
> C 12.0107 C.pbe-rrkjus.UPF
> N 14.0067 N.pbe-rrkjus.UPF
> H 1.00784 H.pbe-rrkjus.UPF
>
> ATOMIC_POSITIONS (crystal)
> Pb 0.992789319 0.992744559 0.978309809
> Pb 0.991367642 0.989878647 0.146751474
> Pb 0.506306111 0.007712595 0.976472657
> Pb 0.504988223 0.004566493 0.144514039
> ....
> ....
> ....
>
> Output:
>
> Voigt approximation:
> Bulk modulus B = 57.08571 kbar
> Young modulus E = 62.26770 kbar
> Shear modulus G = 23.61838 kbar
> Poisson Ratio n = 0.31820
>
> Reuss approximation:
> Bulk modulus B = 82.98611 kbar
> Young modulus E = 11.01452 kbar
> Shear modulus G = 3.72646 kbar
> Poisson Ratio n = 0.47788
>
> Voigt-Reuss-Hill average of the two approximations:
> Bulk modulus B = 70.03591 kbar
> Young modulus E = 36.64111 kbar
> Shear modulus G = 13.67242 kbar
> Poisson Ratio n = 0.33996
>
> Voigt-Reuss-Hill average; sound velocities:
>
> Compressional V_P = 1594.022 m/s
> Bulk V_B = 1419.902 m/s
> Shear V_G = 627.366 m/s
>
> The approximate Debye temperature is 76.616 K
>
> ----------------------------------------
>
> Average Debye sound velocity = 229.337 m/s
>
> Debye temperature = 23.377 K
>
> ********************************************************************
> Input:
>
> &CONTROL
> calculation = "scf"
> ! wf_collect = .true.
> title = 'scf for gap',
> prefix = 'scf',
> restart_mode = 'from_scratch',
> pseudo_dir = '/home/boziki/PP-new/PP/'
> outdir = './'
> nstep = 1000,
> tstress = .true.
> tprnfor = .true.
> /
>
>
> &SYSTEM
> ibrav = 14,
> nat = 144
> ntyp = 5,
> ecutwfc = 40 ,
> ecutrho = 280 ,
> celldm(1) = 34.59613963864875075156
> celldm(2) = 0.49999972688773829727
> celldm(3) = 1.33737830800399180881
> celldm(4) = 0.0
> celldm(5) = 0.0
> celldm(6) = -0.45
> /
>
> &ELECTRONS
> !electron_maxstep = 500,
> conv_thr = 1.d-8
> diagonalization = 'cg'
> /
>
> &IONS
> /
>
> &CELL
> /
>
> K_POINTS automatic
> 2 2 1 1 1 1
>
> ATOMIC_SPECIES
> Pb 1 Pb.pbe-dn-rrkjus_psl.0.2.2.UPF
> I 1 I.pbe-n-rrkjus_psl.0.2.UPF
> C 1 C.pbe-rrkjus.UPF
> N 1 N.pbe-rrkjus.UPF
> H 1 H.pbe-rrkjus.UPF
>
> ATOMIC_POSITIONS (crystal)
> Pb 0.000285166 0.999427499 0.984407789
> Pb 0.999692114 0.000611651 0.151070638
> Pb 0.500287344 0.999428351 0.984408394
> ...
> ...
> ...
>
>
> Output:
>
> Voigt approximation:
> Bulk modulus B = 79.06975 kbar
> Young modulus E = 61.02940 kbar
> Shear modulus G = 22.25142 kbar
> Poisson Ratio n = 0.37136
>
> Reuss approximation:
> Bulk modulus B = 91.94692 kbar
> Young modulus E = -1202.99533 kbar
> Shear modulus G = -163.42392 kbar
> Poisson Ratio n = 2.68060
>
> Voigt-Reuss-Hill average of the two approximations:
> Bulk modulus B = 85.50834 kbar
> Young modulus E = -570.98297 kbar
> Shear modulus G = -70.58625 kbar
> Poisson Ratio n = 3.04458
>
> Voigt-Reuss-Hill average; sound velocities:
>
> The system is unstable for compressional deformations
> Bulk V_B = 11446.859 m/s
> The system is unstable for shear deformations
>
> The approximate Debye temperature not available
>
> ----------------------------------------
>
> Average Debye sound velocity = 1679.234 m/s
>
> Debye temperature = 169.977 K
>
>
>
> Thank you very much in advance for your time.
>
>
> Sincerely yours
>
>
> Ariadni Boziki
>
> EPFL
>
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--
Andrea Dal Corso Tel. 0039-040-3787428
SISSA, Via Bonomea 265 Fax. 0039-040-3787249
I-34136 Trieste (Italy) e-mail: dalcorso at sissa.it
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