[Wien] difference in forces from mini and scf calculations

[Md. Fhokrul Islam]

Hi Marks,

      Thanks for your reply. Let me clarify my question little bit more. 

1) I have optimized the slab using mini. 

2) I have took this optimized case.struct file from mini calculation, initialized  
    a job for wein2k and run scf calculation.

But when I check the force on the same atom here is what I get.

case-1: From mini calculation: 
grep :FGL073 *mini|tail -1
:FGL073:  73.ATOM                 0.233000000     0.045500000     4.378500000 total forces

case-2: From scf calculation: 
grep :FGL073 *scf | tail -1
:FGL073:  73.ATOM                -1.725500000    -0.171500000  -301.077000000 partial forces

My question is why there is difference in force even though in both cases I am using the same
structure. In the 2nd case, I have slightly larger RMT and k points. Is it the reason for this 
difference or I am comparing totally different things.

Thanks,
Fhokrul


Date: Tue, 21 Jun 2011 22:18:38 -0500
From: L-marks at northwestern.edu
To: wien at zeus.theochem.tuwien.ac.at
Subject: Re: [Wien] difference in forces from mini and scf calculations

You do not provide enough information, so all amyone can do is guess.
My guess: you are confusing the valence corrected forces (total at the end of case.scfm) and the uncorrected forces (partial). Mini works with the corrected forces.
On Jun 21, 2011 8:40 PM, "Md. Fhokrul Islam" <fislam at hotmail.com> wrote:
> 
> Hi Prof Blaha,
> 
>     I optimized a slab using mini and it worked fine (forces on atoms were reasonably small) . 

> But when I used the optimized structure from mini calculations and run scf calculations (with 
> energy and charge convergence) the forces on atoms increases even after energy is converged. 
> So my questions are:

> 
> 1. why forces increases even though I am using exactly the same structure from mini calculations?
> 
> 2. how does it effect the calculated properties such as DOS, magnetic moments? I mean should I

>     trust these numbers that I have calculated from scf calculations?
> 
> I have tried looking for the answer in the mailing list but unfortunately I couldn't find one. I would
> appreciate any comment from you.

> 
> 
> Thanks,
> Fhokrul
> 
>  		 	   		  


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