Dear Paolo, Sorry for the late reply, however, I am wondering in this case, how do I calculate the vc-relaxed lattice parameter? If it were cubic I would have multiplied the output CELL_PARAMETER with the lattice and divided by 0.5. But, as it is hexagonal (input) how do I figure out the relaxed lattice parameters? Also, I want to know if the symmetry (hexagonal) has been lost. How do I know the output file retains the input symmetry? The way I do is by looking the the CELL_PARAMETER. But in this case the output CELL_PARAMETER is not exactly representing that of ibrav= 4 but is somewhat closer. Please enlighten me on this; I am struggling a lot.
Thank you! *Bharat Thapa* On Mon, Mar 25, 2019 at 7:27 AM Paolo Giannozzi <[email protected]> wrote: > Is the problem here the loss of the original symmetry of the lattice? if > hexagonal symmetry was present in the starting structure, it isn't lost at > the end (apart from pathological or unfortunate cases). If hexagonal > symmetry was not present in the starting structure, the final lattice may > no longer be hexagonal > > Paolo > > > On Sat, Mar 23, 2019 at 7:05 AM Bharat Thapa <[email protected]> wrote: > >> Dear developer, >> >> >> >> I have vc-relaxed Hf7O8N4 (hafnium oxynitride) assuming the crystal to be >> rhombohedra with a=b, alpha=beta=90 deg, and gamma=120 deg. So, I used >> ibrav=4 and gave A,B,C, cosAB, cosAC and cosBC values. Part of the input >> looks as follows: >> >> >> >> *&system* >> >> * ibrav= 4 * >> >> * A=9.4851, B=9.4851, C=8.7867, cosAB=-0.5, cosAC=0.0, cosBC=0.0* >> >> * nat=19 , ntyp= 3,* >> >> * ecutwfc =70, ecutrho= 840, * >> >> * occupations= 'fixed', * >> >> * nbnd= 100 * >> >> >> >> The vc-relax ran successfully and I got the following output: >> >> >> >> *Final enthalpy = -5322.7186767755 Ry* >> >> *Begin final coordinates* >> >> * new unit-cell volume = 1536.19292 a.u.^3 ( 227.64030 Ang^3 )* >> >> >> >> *CELL_PARAMETERS (alat= 17.92424134)* >> >> * 0.638651125 0.103631841 -0.047929083* >> >> * -0.235833337 0.630643088 -0.049740867* >> >> * -0.043220738 -0.085864416 0.635634338* >> >> >> >> Here, the output cell_parameter values are not consistent with the input. >> I assumed it as ibrav=4 (hex or rhombohedra), but if I use the output >> cell_parameter and calculated the final value (using the vector formulas >> for ibrav=4 from pw.x documentation) for lattice constant ‘a’, I will get >> different values from different vectors. So, my question is how do we >> analyse such a system in which we give certain crystal structure as an >> input and the vc-relax runs successfully (*does not crash*) and give an >> output which isn’t consistent with the input crystal system? Can I accept >> the results and carry on further because the vc-relax did not crash meaning >> that everything is fine? >> >> >> >> Please help me in this regard. >> >> >> >> Kind regards, >> >> >> >> Bharat Thapa >> >> PhD student >> >> UNSW >> _______________________________________________ >> users mailing list >> [email protected] >> https://lists.quantum-espresso.org/mailman/listinfo/users > > > > -- > Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > _______________________________________________ > users mailing list > [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users
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