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[farah marsusi <fmarsusi@yahoo.com>]

Hello Dr. Anglade

could you please send this pdf  text for me too.I am abinit new user . I run both abinit and G03 (B3LYP functional with 6-31G* basis)for H2O molecule ,but the total energy  were different. G03 calculated about 76Ha and abinit about 14Ha.I don't know why?

Herer is my input file.

thanks

F.Marsusi

 

acell   3*30.0 angst

ntypat 2
natom  3
ntypat 1 2 2

znucl  8  1

xangst
 0.000000    0.110843    0.000000 
0.783809   -0.443452    0.000000 
-0.783809   -0.443294    0.000000

nkpt  1

ecut  200 ev

ixc 11

toldfe  5.0d-8

Anglade Pierre-Matthieu <anglade@gmail.com> wrote:

Hi

There is no such "true" ecut:
the cutoff energy describes how many plane waves wil be used to
describe the wave functions within your calculations. The more plane
waves the more frequencies will be depicted and then the more accurate
will be your calculation.
You have to find an equilibrium between the computation time and the
accuracy of your calculation. That's why we usually search the minimum
ecut that accurately describe the system. Here "accurately" may
strongly depends on the properties you want to examine. If you have no
special requirement an absolute convergence of about 1e-3 Ha is
usually considered correct because pseudopotentials tends to reproduce
the full electron calculation on which they are based to this
precision. That is, you will (almost) never get more physics by having
something better converged. However some problems may require
convergency of ecut down to 1e-4 or 1e-5 Ha.

You can find examples of how to find the correct value of ecut in the
Abinit tutorials. HAve you tryed them and reproduce the steps depicted
there in your calculations ? If you want some comments on your own
results, please send some details about your input and output.

Also, I'm just back from a summer school where I have presented
Abinit to very beginners in DFT - PW calculations. Then, I have lots
of didactical materials where I insist on this very problem. If you
like I can send those PDF to you.

regards

pierre-matthieu Anglade

On 8/2/07, m_mousavi1980@yahoo.com wrote:
>
> Hi
>
> I have a question
> How can i understand which ecut for zno is true.
> I get ecut 62.01
> thanks
> best regard
>


--
Pierre-Matthieu Anglade

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