>
> To control the predefined "meaningful energy DIFFERENCES", which
> parameter(s)/flag(s) you refer to in the fdf file?
>
> Regards
This is not in the flags; this is human's part of job
("to know what you are doing").
To give you an example:
when comparing energies of two different phases
we'd probably deal with another scale of
"meaningful energy DIFFERENCE"
than when comparing two different orientations of a given spin
(although who knows...)
Best regards
Andrei Postnikov
> On 08/04/2011 03:59 AM, [email protected] wrote:
>>> On 08/04/2011 02:17 AM, [email protected] wrote:
>>>> 2. You can eventually extract total energies, make a plot and
>>>> look at it, but attention! It is IMPOSSIBLE to decide whether the
>>>> energy
>>>> is "converged" or not without specifying the relevant order of
>>>> magnitude
>>>> of DIFFERENCES you are interested in to study, like e.g. the effect of
>>>> atom displacement, changing magnetic configuration, imposing pressure,
>>>> etc.
>>>
>>> For total energies, this can be controlled by
>>> DM.Require.Energy.Convergence and DM.Require.Energy.Convergence. But
>>> in
>>> fact, in default case, the siesta don't use this convergence criteria.
>>> Regards
>>> --
>>> Hongyi Zhao<[email protected]>
>>
>> This seems to be a misunderstanding. The convergence entries you refer
>> to,
>> along with some others, determine when the program converges
>> after a certain number of iterations and stops
>> FOR THE GIVEN PARAMETERS as MeshCutoff, k-mesh density, basis size, etc.
>> This does not give you any hint as to whether these parameters
>> are "good". Whatever was referred to before (and in the mailing list,
>> and in the tutorials) in the present context as convergence with respect
>> to these calculation parameters is different.
>> What was meant is the following:
>> you take some MeshCutoff, converge the calculation,
>> write down the value. You change MeshCutoff, you converge the
>> calculation,
>> write down the value. Then you have a look at a sequence of converged
>> values you wrote down and try to figure out which value of MeshCutoff
>> is sufficient, or "converged", in a sense that its further changing
>> does not affect the result. The problem hereby: you cannot decide on
>> this
>> unless you know IN ADVANCE which accuracy you in fact need, i.e.,
>> meaningful energy DIFFERENCES for your problem.
>
> To control the predefined "meaningful energy DIFFERENCES", which
> parameter(s)/flag(s) you refer to in the fdf file?
>
> Regards
>> This was the meaning of my comment.
>>
>> Best regards
>>
>> Andrei Postnikov
>>
>>
>>
>
>
> --
> Hongyi Zhao <[email protected]>
> Institute of Semiconductors, Chinese Academy of Sciences
> GnuPG DSA: 0xD108493
>
>
