[Wien] Phonon difficulties

[Peter Blaha]

I do not see a problem in the forces. Of course, when displacing an atom, it will
have a large force (opposite to its displacement), and all other atoms will have
small forces too.

Testing k-mesh and RKmax is always a "second" step. I.e. caclculate the phonons with
this set, then repeate the calculations with more k-points and larger kkmax und compare
the resulting phonons. If changes are small, you have converged results.

I don't think you need   -fc 0.004 mRy;   at first -fc 0.1 will do, eventually try
-fc 0.01

MUCH MORE IMPORTANT is the size of your supercell. With 16 atom cells, the phonons on
general k-points can be COMPLETELY wrong (and rkmax,... does not help)

Am 12.02.2011 07:38, schrieb Ghosh SUDDHASATTWA:
> The number of k-points seems to be too low (I guess, but I may be wrong)
>
> Improve the k-mesh
>
> Increase the rk_max
>
> Improve the force convergence(0.004 mRy)
>
> Are u running –sp- phonon calculation?
>
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> *From:*wien-bounces at zeus.theochem.tuwien.ac.at [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] *On Behalf Of *puday at iitk.ac.in
> *Sent:* Saturday, February 12, 2011 9:01 AM
> *To:* A Mailing list for WIEN2k users
> *Subject:* [Wien] Phonon difficulties
>
> Dear Prof. Blaha and wien2k users,
>
> I am doing phonon calculation for the given example in the manual "AlNi" I
> have used supercell 2x2x2 and displacement of atom 0.03 Angstrom by
> default. It is taking the displacement of the atoms 8 and 9 in the
> "AlNi.d45" as
>
> 0.005186 0.000000 0.000000 Al 8
> 0.005186 0.000000 0.000000 Ni 9
>
> And see the forces bellow for the atom 8th Al and 9th Ni.
> It is giving huge forces in all direction particularly Fx. And force
> constant plot gives negative values.Here is my AlNi.dat file please see
> it.
>
>
> ----------------------------------------------------------------------------
> ! Phonon-file by phonon2wien2k from AlNi.d45
> ! :RKM : MATRIX SIZE 1365LOs: 152 RKM= 6.97 WEIGHT= 1.00 PGR:
> ! :KPT : NUMBER OF K-POINTS: 112
> 5.784714 0.000000 0.000000
> 0.000000 5.784714 0.000000
> 0.000000 0.000000 5.784714
> 0.2500000 0.2500000 0.2500000 0.0051860 0.0000000
> 0.0000000
> 1 A 0.7500000 0.7500000 0.7500000 0.2400 -0.0070 0.0020
> 2 A 0.2500000 0.7500000 0.7500000 0.1280 -0.0560 -0.0420
> 3 A 0.7500000 0.2500000 0.7500000 -0.2400 0.0090 -0.0380
> 4 A 0.2500000 0.2500000 0.7500000 0.4160 0.0570 -0.0070
> 5 A 0.7500000 0.7500000 0.2500000 -0.2440 -0.0490 0.0000
> 6 A 0.2500000 0.7500000 0.2500000 0.4230 -0.0170 0.0480
> 7 A 0.7500000 0.2500000 0.2500000 1.7240 0.0420 0.0300
> 8 A 0.2500000 0.2500000 0.2500000 -8.2650 0.0130 0.0050
> 9 N 0.0000000 0.0000000 0.0000000 0.7010 0.3900 0.3880
> 10 N 0.5000000 0.0000000 0.0000000 0.7680 -0.5280 -0.5150
> 11 N 0.0000000 0.5000000 0.0000000 0.7000 -0.3810 0.3810
> 12 N 0.5000000 0.5000000 0.0000000 0.7610 0.5210 -0.5240
> 13 N 0.0000000 0.0000000 0.5000000 0.7000 0.3790 -0.3840
> 14 N 0.5000000 0.0000000 0.5000000 0.7590 -0.5280 0.5120
> 15 N 0.0000000 0.5000000 0.5000000 0.7110 -0.3790 -0.3790
> 16 N 0.5000000 0.5000000 0.5000000 0.7290 0.5260 0.5230
> 0.0000000 0.0000000 0.0000000 0.0051860 0.0000000
> 0.0000000
> 1 A 0.7500000 0.7500000 0.7500000 0.7300 0.4470 0.4620
> 2 A 0.2500000 0.7500000 0.7500000 0.7300 -0.6140 -0.5990
> 3 A 0.7500000 0.2500000 0.7500000 0.7390 -0.4440 0.4630
> 4 A 0.2500000 0.2500000 0.7500000 0.7140 0.6120 -0.5980
> 5 A 0.7500000 0.7500000 0.2500000 0.7390 0.4520 -0.4590
> 6 A 0.2500000 0.7500000 0.2500000 0.7160 -0.6110 0.5960
> 7 A 0.7500000 0.2500000 0.2500000 0.7520 -0.4480 -0.4620
> 8 A 0.2500000 0.2500000 0.2500000 0.6970 0.6090 0.5990
> 9 N 0.0000000 0.0000000 0.0000000 -5.6470 -0.0200 -0.0170
> 10 N 0.5000000 0.0000000 0.0000000 -0.2730 0.0150 0.0150
> 11 N 0.0000000 0.5000000 0.0000000 -0.0710 0.0210 0.0390
> 12 N 0.5000000 0.5000000 0.0000000 0.4970 -0.0240 -0.0400
> 13 N 0.0000000 0.0000000 0.5000000 -0.0650 0.0400 0.0200
> 14 N 0.5000000 0.0000000 0.5000000 0.4970 -0.0410 -0.0260
> 15 N 0.0000000 0.5000000 0.5000000 -0.7700 -0.0340 -0.0330
> 16 N 0.5000000 0.5000000 0.5000000 -0.0010 0.0420 0.0400
> ----------------------------------------------------------------------------
>
>
> What should I do to resolve it?Please help me in this regard.Any help will
> be very helpfull for me.
>
> reds,
> Uday
> Research scholar
> Dept.of Physics
> IIT Kanpur
> India
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-- 
-----------------------------------------
Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: pblaha at theochem.tuwien.ac.at
-----------------------------------------