[Wien] Fwd:
Peter Blaha
pblaha at theochem.tuwien.ac.at
Thu May 2 20:36:03 CEST 2019
Do you think the structure you generated is a "statistical" occupation ???
You need to generate bigger supercells (without a preferred direction as
in your trial structure) and bring some "randomness" into the
occupations. The smallest cell I would accept is a 2x2x2 supercell. And
you can try different distributions. Maybe you find by E-tot comparisons
some preferred neighborhood ....
PS: Due to the substitution you will of course break symmetry and no
longer have P6/mmm. But usually you can use nn instead of sgroup to find
equivalent atoms and keep the hexagonal unit cell (when the number of
non-equivalent atoms and the number of symmetry operations are
identical, there is no need to use the cell generated by sgroup).
Am 02.05.2019 um 03:07 schrieb Anup Shakya:
> Dear All,
>
> I am doing calculations on a material Nd2PdSi3 which is of AlB2
> hexagonal structure (space group P6/mmm) with lattice constants a=b=
> 4.103 ang and c = 4.204 ang. The positions of the atoms are as follows:
> R 1a site 0 0 0 and Pd and Si statistically distributed on the 2d site
> 1/3 2/3 1/2 with 25 % and 75% respectively. I started making the
> structure using R at 1a site and Si at 2d site, so I get one Nd atom and
> two Si atoms.
>
> Title
> H LATTICE,NONEQUIV.ATOMS: 2 191_P6/mmm
> MODE OF CALC=RELA unit=ang
> 7.754116 7.754116 7.944223 90.000000 90.000000120.000000
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000
> MULT= 1 ISPLIT= 8
> Nd NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 60.000
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 2: X=0.33333333 Y=0.66666667 Z=0.50000000
> MULT= 2 ISPLIT= 8
> ATOM 2:X= 0.66666667 Y=0.33333333 Z=0.50000000
> Si NPT= 781 R0=0.00010000 RMT= 2.2200 Z: 14.000
> LOCAL ROT MATRIX: 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> 0 NUMBER OF SYMMETRY OPERATIONS
> ~
> In order to make the ratio of Pd:Si as 1:3, I have doubled the structure
> along x axis using the super cell program, The structure is shown below:
>
> Title
> P LATTICE,NONEQUIV. ATOMS 4
> MODE OF CALC=RELA unit=ang
> 15.508232 7.754116 7.944223 90.000000 90.000000120.000000
> ATOM 1: X=0.00000000 Y=0.00000000 Z=0.00000000
> MULT= 1 ISPLIT= 8
> Nd NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 60.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 2: X=0.50000000 Y=0.00000000 Z=0.00000000
> MULT= 1 ISPLIT= 8
> Nd NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 60.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM 3: X=0.16666666 Y=0.66666667 Z=0.50000000
> MULT= 2 ISPLIT= 8
> ATOM 3: X=0.33333334 Y=0.33333333 Z=0.50000000
> Si NPT= 781 R0=0.00010000 RMT= 2.2200 Z: 14.0
> LOCAL ROT MATRIX: 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> ATOM 4: X=0.66666666 Y=0.66666667 Z=0.50000000
> MULT= 2 ISPLIT= 8
> ATOM 4: X=0.83333334 Y=0.33333333 Z=0.50000000
> Si NPT= 781 R0=0.00010000 RMT= 2.2200 Z: 14.0
> LOCAL ROT MATRIX: 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> 0.0000000 0.0000000 0.0000000
> 0 NUMBER OF SYMMETRY OPERATIONS
>
> After this I splitted the 2nd atomic position of the 3rd Si atom and
> then changed the atom from Si to Pd and the Z value to 46 i.e, for Pd
> and then saved the structure.
>
> When I initialized I got the following warning:
> SUMS TO 4.44000 LT. NN-DIST= 4.47684
> WARNING: Mult not equal. PLEASE CHECK outputnn-file
> WARNING: ityp not equal. PLEASE CHECK outputnn-file
> WARNING: ityp not equal. PLEASE CHECK outputnn-file
>
> Then I accepted the structure given by x sgroup and I get the following
> struture
>
> Title
> P LATTICE,NONEQUIV.ATOMS: 6 25 Pmm2
> RELA
> 7.754116 7.944223 13.430523 90.000000 90.000000 90.000000
> ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000
> MULT= 1 ISPLIT= 8
> Nd1 NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 60.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -2: X=0.50000000 Y=0.00000000 Z=0.50000000
> MULT= 1 ISPLIT= 8
> Nd2 NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 60.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -3: X=0.49999999 Y=0.50000000 Z=0.83333334
> MULT= 1 ISPLIT= 8
> Pd1 NPT= 781 R0=0.00001000 RMT= 2.5000 Z: 46.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -4: X=0.00000000 Y=0.50000000 Z=0.33333334
> MULT= 1 ISPLIT= 8
> Si1 NPT= 781 R0=0.00010000 RMT= 1.8900 Z: 14.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -5: X=0.50000001 Y=0.50000000 Z=0.16666666
> MULT= 1 ISPLIT= 8
> Si2 NPT= 781 R0=0.00010000 RMT= 1.8900 Z: 14.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> ATOM -6: X=0.00000000 Y=0.50000000 Z=0.66666666
> MULT= 1 ISPLIT= 8
> Si3 NPT= 781 R0=0.00010000 RMT= 1.8900 Z: 14.0
> LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000
> 0.0000000 1.0000000 0.0000000
> 0.0000000 0.0000000 1.0000000
> 4 NUMBER OF SYMMETRY OPERATIONS
> 1 0 0 0.00000000
> Now the question is my initial experimental structure was AlB2 hexagonal
> type but since I could not have Pd and Si distribution in this structure
> in 1:3 ratio I made a supercell and the structure which I have generated
> now is Pmm2 structure which is orthorhombic but has a distribution of Pd
> and Si in 1:3 ratio. Is it ok to perform calculations on this structure?
>
> Secondly, I want to perform Antiferromagnetic calculations with
> different magnetic configurations like A, C, G type and for that I have
> to further increase the supercell. That in itself will further change
> the symmetry. Can I use this structure and make a super cell to define
> the magnetic configuration for the Nd ion?
> Please suggest.
>
> Sincerely,
> Anup Pradhan Sakhya (Ph.D.)
> Visiting Post-Doctoral Fellow
> DCMP&MS, TIFR, Mumbai
>
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--
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671
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