[Wien] small organic molecules (12 atoms): ? convergence criteria and number of points

[Peter Blaha]

> I am calculating electronic structure of isolated benzene molecules (C6H6)
> 
> I have managed to run SCF cycles with the values of 
> convergence paramerters: charge convergence 0.01 electron charge,
> and NPT (struct gen) 61and
> number of points for kgen 61
> (RKMAX was 3 and 4 and 5)

Please do NOT change the default NPT values! w2web provides you with a 
reasonable mesh (suitable for GGA calculations). If you go through the
TiC "getting started" example, you get an indication what the userdefinable
parameters are:
RMT: For your example you should set RMT(H) about RMT(C)/2 ! (Read the FAQ
     page on www.wien2k.at/reg_user
RKMAX: usually reasonable values start at 5 and go up to 9. Again only for
     your C-H bonds: RKMAX=3-4 is probably enough.
k-points: K-points come from the periodic boundaries in solids.....
     If you simulate a molecule (in a large box, did you choose some
     tetragonal (or hexagonal) box, so that the distances between neighboring 
     molecules is comparable in x,y,z direction ?) ONE k-point is enough!
     (You should NOT have any k-dispersion in a molecule! 

Regards
                                      P.Blaha
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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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