[Pw_forum] About F_QHA.x

[Eyvaz Isaev]

Dear Amit, 

Can you please send me your IFC file so I can test it?

Bests,
Eyvaz.

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Prof. Eyvaz Isaev, 

Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com

--- On Mon, 5/24/10, Yamit <amit99266 at rediffmail.com> wrote:

From: Yamit <amit99266 at rediffmail.com>
Subject: [Pw_forum] About F_QHA.x
To: pw_forum at pwscf.org
Date: Monday, May 24, 2010, 5:01 PM

Dear All



I have attempted to calculate the specific heat of Si using "F_QHA.x", and the calculated Silicon phonon dos  as an input.

(The calculated Si phonon frequencies are in excellent agreement with available experimental data. )



As the output of "F_QHA.x", I have obtained the following results, (in QHA.out file)



############################################################################################################



# T in K, F_vib in Ry/cell, C_v in R (the universal gas constant by 3N modes), S in k_B

############################################################################################################

#   T         E_internal        F_vibration          Specific heat (C_v)       Entropy

############################################################################################################

:

:

  295.00      0.0139740852      0.0055747646           4.6621714979          4.4956255367

 300.00      0.0141222695      0.0054311560           4.6966380876          4.5742737931

 305.00      0.0142715257      0.0052850687           4.7298757363          4.6521815403

 310.00      0.0144218157      0.0051365259           4.7619351485          4.7293532915

:

:

:

############################################################################################################



From the above results, at 300 K:



4.6966380876  * 8.314 = 39.048

(where, Gas constant, R = 8.314 J/(mol K) ) and for Silicon N = 2, so 3N=6 modes



So, Specific heat, C_v= 38.761 / 3N = 6.5080  J/(mol K)



Experimentally the Specific heat, C_v of Si at 25 °C (~298) is found equal to 9.789 J·mol−1·K−1. 



Can anybody could explain the reason behind this huge error in the calculation of specific heat ?



Warm Regards

Amit N. Harode

C R Labs INDIA



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