On Mon, 8 Jul 2019 at 9:15 pm, Bharat Thapa <[email protected]> wrote:
> 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 > > -- *Bharat Thapa*
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