[Wien] FW: Internal Coordinates minimization for Monoclinic

[Ghosh SUDDHASATTWA]

Dear Prof.Blaha, 
Extending the discussion on internal coordinates minimization and structure
optimization, I have a tetragonal body centered lattice with 58 atoms per
unit cell and 8 inequivalent atoms. 
We can use suitable options in the optimization (c/a). Since, the number of
atoms are large enough, can we go in for min_lapw with similar arguments you
mention for monoclinic lattice. 
I ask this question as my total run time for SCF (-ec 0.0001 -cc 0.0001
-in1ef) on 32 cpu's is more than 7 days. 
So, is it advisable to do only min_lapw 

I am not asking for any shortcuts, Dear users, 

Suddhasattwa Ghosh 



-----Original Message-----
From: wien-bounces at zeus.theochem.tuwien.ac.at
[mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha
Sent: Monday, June 28, 2010 12:40 PM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] FW: Internal Coordinates minimization for Monoclinic

You are comparing apples and bananas.

With min_lapw you optimize internal atomic positions, at given (fixed)
lattice
parameters. So you can only say, you have an "optimum structure" with
respect to fixed
(experimental) lattice parameters.
Often, this is a VERY good strategy, since experimental a,b,c are MUCH MORE
accurate
than theoretical ones, while for atomic positions often the opposite holds.
Note, however, you CANNOT use -so for force optimization.

With the first approach, you can try to find optimal a,b,c,gamma lattice
parameters. However, usually it is also very important to optimize internal
coordinates simultaneously, because this may also influence a,b,c...
As mentioned above, theory is usually quite bad on that and for a monoclinic
structure this gets expensive.

> I have done the following 
> 1. Generate the structure file and run a normal SCF with spin orbit
> coupling. (Since I am working on an heavy element with 18 atoms per unit
> cell)
> 2. Now my question is 
> We can either use option 7 and generate 15 structures and optimize the
> structure with minimum energy. 
> By modifying the command in optimize.job 
> Run_lapw -cc 0.0001 -ec 0.0001 -p -so 
> 
> Or, we can simply do min_lapw for the structure file we have generated
> initially. 
> After running min_lapw, we get the atomic positions with minimum partial
> forces, which gets saved in the structure file. 
> Now, using the revised (optimized) atomic coordinates, run a SCF. 
> By doing so, can we say that we have the structure with minimum total
energy
> (by doing only min_lapw and not using option 7) 
> 
> I hope I am clear enough now. 
> Thank you 
> Suddhasattwa 
> 
> -----Original Message-----
> From: wien-bounces at zeus.theochem.tuwien.ac.at
> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Peter Blaha
> Sent: Monday, June 28, 2010 11:02 AM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] FW: Internal Coordinates minimization for Monoclinic
> 
> Most likely nobody can answer this question, because nobody understands
your
> question.
> At least I did not understand what you are really doing.
> 
> Did you run    x optimize with option 7 ?
> Did you modify optimize.job or just run it unmodified ?
> Did you put min_lapw instead or run_lapw ?
> Did you find the structure with lowest total energy ?
> 
>> Coming back to my question, doing a 4-D optimization of a monoclinic 
>> case by choosing Option 7, can we say with authority that
>>
>> 1. Internal coordinates minimization of monoclinic case (with 18 atoms 
>> per unit cell) keeping the lattice parameters same would be enough to 
>> know the total energy.
>>
> 
>> In any case, after lapw_mini, the optimized coordinates are saved in the 
>> case.struct, so running the SCf again would give the optimized total 
>> energy.
> 
> Why would you run again an scf ? You already have one ?
> 
> 

-- 

                                       P.Blaha
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW:
http://info.tuwien.ac.at/theochem/
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