[Wien] question

[Stefaan Cottenier]

> In the scf calculation of TiC, the amount of force in case.scf is 44.28
> (mRid/a.u). Is its means that the TiC structure is under pressure?? what
> should I do for give the force bellow 5 (mRyd/a.u)?

Something must be wrong here. TiC (with space group Fm-3m) cannot have 
forces (symmetry-forbidden).

Furthermore, don't confuse forces (=on individual atoms) with pressure 
(=on the entire cell).

Forces can be minimized by moving atoms (min_lapw). Pressure can be 
minimized by changing the cell volume (and sometimes cell shape -- x 
optimize).

See the UG for more details.

Stefaan


> --- On *Sat, 1/19/13, Stefaan Cottenier /<Stefaan.Cottenier at UGent.be>/*
> wrote:
>
>
>     From: Stefaan Cottenier <Stefaan.Cottenier at UGent.be>
>     Subject: Re: [Wien] [SPAM] Re: question
>     To: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
>     Date: Saturday, January 19, 2013, 6:23 AM
>
>
>      > How much should be the amount of force for optimized structure? in my
>      > example, the force is 44.28 (mili Rydberg/ bohr) for TiC structure.
>      > what is the acceptable amount of force for the relaxed structure?
>     Is it
>      > 5 miliRydberg/bohr?
>
>     It depends on what you're interested in. For phonon calculations,
>     forces should be better than 1 mRy/au. For the E(V)-curve, 5 mRy/au
>     is often sufficient.
>
>     In general: inspect how your property of interest (:ENE, :EFG, ...)
>     depends on the forces.
>
>     Stefaan
>
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