[Pw_forum] problem of the second derivative of energy of DFPT

[Wei He]

Dear Stefano

	You are right, thank you. I have missed {crystal} in the
input file, which makes me confused on the direction of displacement.

Best Wishes
Wei He

	

======= 2004-01-07 21:08:04 =======

>using your input I get:
>
>0.190 Ryd/bohr2 from energy vs displacement of frozen phonon
>0.193 Ryd/bohr2 from force vs displacement of frozen phonon
>0.191 Ryd/bohr2 from diagonal element of dynamical matrix computed by
>phonon code.
>
>pay attention that in your input alas.dx.scf.in the atom is displaced by
>0.001 in the 111 direction so the lenght of your displacement is 10.60 *
>0.001 * sqrt(3) bohr. I guess you overlooked that (0.571/3=0.190).
>I don't know why you get 0.203 from the phonon calculation.
>
>Stefano de Gironcoli
>
>
>贺伟 wrote:
>
>>Dear PWSCF user
>>
>>	I want to get the second derivatives of Born-Oppenheimer energy surface,
>>but I found that dinsity functional perturbation mothod gave different result 
>>than the stupid finite difference method.
>>
>>	My testing system is the AlAs bulk. In finite difference method, I first
>>did a scf calculation with the relaxed geometry. Then I moved Al atom 1/1000 
>>of celldm(1) along x and -x directions, and did scf calculations again. The 
>>resulting three energies gave a FD second derivative of energy as 0.571 Ryd/Bohr^2. 
>>But DFTP gave the second derivative as 0.203 Ryd/Bohr^2 (the first element of 
>>the dynamic matrix).
>>
>>	Can anybody give me some suggestion? Thanks! I have attach the input files 
>>with this email. 
>>
>>Best Wishes
>>Wei He 	
>>
>
>
>
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　　　　　　　　致
礼！
 
				 
　　　　　　　　Wei He
　　　　　　　　weihe at mail.ustc.edu.cn
　　　　　　　　　　2004-01-07