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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

Hello Guangfu Luo,

First of all, I don't understand why it would be different to send an attachment to the forum. Several other people have said the same, but it is just an email address...

Anyhow, having looked at your (very systematic and clear) outputs, and comparing the tnlo_2.out files, you can see at the end the block  ==> Compute Derivative Database <==. This contains the 2dTE for all the perturbations which were actually calculated, _plus_ those which come from non-stationary expressions (NSE) of the 2dTE (see Xavier's prb_55_10337 and following paper with Changyol Lee). 

The NSE allow you to calculate the derivative of E_tot wrt R_alpha and R_beta, if you are given just the derivatives of the potentials wrt R_alpha only (which abinit just calculated). In this way, from just the perturbations wrt 1 atom, you can complete whole rows and columns of the full interatomic force constant (IFC) matrix.

However, the non-stationary expressions are less precise, and in your case I believe that they are completely off (sometimes by a factor of 2), probably because of the very low ecut (I can't see any other unconverged parameters). As a result, all of the calculations you did (Usual, and merged) are roughly at the same level of convergence, but the way the IFC matrix is completed was different, because of different errors in the NSE, and they give different results at the end (during the mergeddb the 2dTE are now overcomplete, and I don't know which values mrgddb will choose to prefer - those coming from Part1 or Part2, or an average...).

Could you try an ecut-converged calculation to see if this is indeed the case?

Matthieu

---------- Forwarded message ----------
From: Guangfu Luo <6671011@163.com>
Date: 2009/3/7
Subject: Re: [abinit-forum] Possible method to speed RF calculation?
To: matthieu.jean.verstraete@gmail.com

Dear Matthieu,

 

Because I do not know how to attach enclosure to the Forum, I send the two-atom test directly to you. The files come from the built-in tests after a little revision.

 

 

The structure of the tar file is,

(1) UsualMethod means "rfatpol 1 2"

 

(2) Part1 and Part2 mean "rfatpol 1 1" and "rfatpol 2 2", respectively.

(3) MergePart1-2_andthen_AnalyseIR means merge the DDBs from Part1 and Part2 and then analyze the IR.

 

 

I compared their spectra of "Oscillator strengths", and found (1) show two distinct peaks, while the (2)-(3) method shows only one peak (or two nearly degenerate peaks).

 

Thanks

 

 

Sincerely,

Guangfu Luo

 

2009-03-08，"matthieu verstraete" <matthieu.jean.verstraete@gmail.com> wrote：

In principle yes, 2 atoms should be the same. Send in your in/output for the test cases.

Matthieu

On Sat, Mar 7, 2009 at 6:33 PM, <6671011@163.com> wrote:

Dear friends,

During a RF calculation, if one wants to do the perturbations of n atoms,
usually he/she calculates them in a single file by using rfatpol 1 n.


I wonder if we can speed the RF calculation by splitting it into several
separate files, such as
    file1: rfatpol 1  i
    file2: rfatpol i+1 j
    file3: rfatpol j+1 n
Then the files can be submitted at the same time; when they finish, one can
merge their DDBs.


I tested the forementioned methods in several systems, and most of them give
almost the same results, except a two-atom system.  My question is: are the two
ways equivalent in principle?


Thanks.

Sincerely,
Gunagfu Luo

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500

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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390

Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500

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