[Wien] Volume optimization of Sulphur
shamik chakrabarti
shamik15041981 at gmail.com
Tue Mar 10 13:17:39 CET 2020
Dear Prof. Blaha,
Thank you so much for your elaborate reply. This
will be very helpful for me.
Thanks once again.
with regards,
On Tue, 10 Mar 2020 at 17:23, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:
> I think F. Tran already gave you the hint about "primitive R cell" and
> "conventional H cell".
>
> The volume of the R cell is 3 times smaller than that of the H cell.
>
> Wien2k gives H lattice parameters, but makes the calculation internally
> in R cell.
>
> So yes, if you get an equilibrium volume which does not fit your
> expectations, it is because of your wrong assumptions aber the actual
> lattice.
>
> It is the same as for a FCC cubic cell: What is the volume of the
> primitive (R) cell of an FCC lattice: it is NOT a**3, but a**3 / 4.
>
> --------------------
> Besides this: the optimize scribt gives you a volume, but of course also
> total energies and you can easily see, which of your struct files
> corresponds (nearly) to the optimized volume (the one with the lowest
> energy). And you find the corresponding a,c values directly in this
> struct file.....
>
> It can't be that difficult to get the optimized lattice parameters.
>
> PS: Please read the UG (struct file) about R-lattices
>
> On 3/10/20 11:03 AM, shamik chakrabarti wrote:
> > I think we should multiply the printed volume by 3 to get the actual
> > volume as the cell described in rhombohedral lattice is 3 times larger
> > than the hexagonal unit cell...I am sending a link which gives this clue
> >
> > http://www.globalsino.com/EM/page3546.html
> >
> > Please correct me if I am wrong!
> >
> > with regards,
> >
> > On Tue, 10 Mar 2020 at 15:22, Tran, Fabien <fabien.tran at tuwien.ac.at
> > <mailto:fabien.tran at tuwien.ac.at>> wrote:
> >
> > Probably. In case.struct, the lattice constants and angles are for
> > the hexagonal cell, while atoms positions are with respect to
> > rhombohedral.
> >
> >
> >
> ------------------------------------------------------------------------
> > *From:* Wien <wien-bounces at zeus.theochem.tuwien.ac.at
> > <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> on behalf of
> > shamik chakrabarti <shamik15041981 at gmail.com
> > <mailto:shamik15041981 at gmail.com>>
> > *Sent:* Tuesday, March 10, 2020 10:46 AM
> > *To:* A Mailing list for WIEN2k users
> > *Subject:* Re: [Wien] Volume optimization of Sulphur
> > It may be a clue for solving the above problem;
> >
> > In the struct file (as seen in the GUI) a line
> > remains added : "positions must be specified in rhombohedral
> > coordinates!"
> >
> > Looking forward to your response eagerly.
> >
> > with regards,
> >
> > On Tue, 10 Mar 2020 at 14:51, shamik chakrabarti
> > <shamik15041981 at gmail.com <mailto:shamik15041981 at gmail.com>> wrote:
> >
> > Dear Prof. Tran,
> >
> > a^2 c Sin 60 is the volume of the
> > rhombohedral cell having lattice parameter a=b & c. I have used
> > the same formula for hexagonal SnS2 and got very good results. I
> > think somehow the printed volume is almost 1/2.8 th of the
> > actual value needed. I guess it is something related to R_3
> > crystal system...........
> >
> > with regards,
> >
> > On Tue, 10 Mar 2020 at 14:36, Tran, Fabien
> > <fabien.tran at tuwien.ac.at <mailto:fabien.tran at tuwien.ac.at>>
> wrote:
> >
> > WIEN2k does the calculations in the primitive unit cell,
> > whose volume is given by :VOL in case.scf
> >
> > Is a^2 c Sin 60 not the volume of the conventional cell?
> >
> > You can visualize the primitive and conventional cells of
> > case.struct with xcrysden (press F3 or F4).
> >
> >
> >
> ------------------------------------------------------------------------
> > *From:* Wien <wien-bounces at zeus.theochem.tuwien.ac.at
> > <mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> on behalf
> > of shamik chakrabarti <shamik15041981 at gmail.com
> > <mailto:shamik15041981 at gmail.com>>
> > *Sent:* Tuesday, March 10, 2020 9:58 AM
> > *To:* A Mailing list for WIEN2k users
> > *Subject:* Re: [Wien] Volume optimization of Sulphur
> > Dear Wien2k users,
> >
> > I am also certain that I am
> > not doing any mistake in the formula of Volume=a^2 c Sin
> > 60. However, the V0 printed in the window showing the fitted
> > BM curve is coming much less than that expected from a^2 c
> > Sin 60 . What could be the cause? Is it related to the space
> > group R_3 (space group no. 148)?
> >
> > Looking forward to your reply eagerly.
> >
> > with regards,
> >
> >
> > On Tue, 10 Mar 2020 at 13:11, shamik chakrabarti
> > <shamik15041981 at gmail.com <mailto:shamik15041981 at gmail.com>>
> > wrote:
> >
> > Dear Lyudmila Sir,
> >
> > To remove the confusion I am
> > sending the struct file which have been used in our
> > simulation. I have good results as far as the volume
> > optimization curve is concerned. However, while
> > calculating the lattice parameters using the formula V =
> > a^2 c sin60 I got the low value of lattice parameters.
> > My query is
> > (1) Whether I have done something wrong in the formula
> > itself?
> > (2) While GGA is better than nlvdw in this case?
> >
> > with regards,
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
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> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> > _______________________________________________
> > Wien mailing list
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> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> > _______________________________________________
> > Wien mailing list
> > Wien at zeus.theochem.tuwien.ac.at
> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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> >
>
> --
>
> P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
> WWW: http://www.imc.tuwien.ac.at/TC_Blaha
> --------------------------------------------------------------------------
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--
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
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