# [Pw_forum] about C2/c point group symmetry of a monoclinic lattice.

Mutlu COLAKOGULLARI mutlucolakogullari at trakya.edu.tr
Wed Dec 17 14:08:12 CET 2014

```Dear All,
I am working on a monoclinic material which has space group 15. It has C2/c point group.
When I run the pwscf, it gives me the C2/m point group that corresponds to the space group 12.
point group C_2h (2/m)
there are  4 classes
the character table:
E     C2      i     s_h
A_g    1.00  1.00  1.00  1.00
B_g    1.00 -1.00  1.00 -1.00
A_u    1.00  1.00 -1.00 -1.00
B_u    1.00 -1.00 -1.00  1.00
The symmetry operations of these two monoclinic space groups have 8 symmetry operations.  pwscf symmetry calculations found just 4...what about the other 4?
I have checked the space groups  from "http://www.cryst.ehu.es/cryst/get_gen.html":
General Positions of the Group 12 (C2/m) [unique axis b]
1. x,y,z
2. -x,y,-z
3. -x,-y,-z
4. x,-y,z
5. x+1/2,y+1/2,z
6. -x+1/2,y+1/2,-z
7. -x+1/2,-y+1/2,-z

8. x+1/2,-y+1/2,z
General Positions of the Group 15 (C2/c) [unique axis b]
1. x,y,z
2. -x,y,-z+1/2
3. -x,-y,-z
4. x,-y,z+1/2
5. x+1/2,y+1/2,z
6. -x+1/2,y+1/2,-z+1/2
7. -x+1/2,-y+1/2,-z
8. x+1/2,-y+1/2,z+1/2
Here is the lite-input:

&control
calculation  = 'scf',
restart_mode = 'from_scratch',
pseudo_dir   = '/home//tlg2/pseudos',
outdir       = './outdir',
prefix       = 'TlGaSe2',
verbosity    = 'high'

/

&system
ibrav = -13

celldm(1)=20.166973593
celldm(2)=0.999721681046
celldm(3)=1.453103256
celldm(5)=-0.173527859407
nat              = 32
ntyp             = 3
ecutwfc          = 65
ecutrho          = 650
/
&electrons
diagonalization = 'david'
diago_david_ndim  = 8
mixing_mode      = 'plain'
mixing_beta      = 0.7
mixing_ndim      = 8
conv_thr         = 1.0d-8,
/

ATOMIC_SPECIES
Tl   204.3833  Tl.pbesol-dn-rrkjus_psl.1.0.0.UPF
Ga    69.7230  Ga.pbesol-dn-rrkjus_psl.1.0.0.UPF
Se    78.9600  Se.pbesol-dn-rrkjus_psl.1.0.0.UPF
ATOMIC_POSITIONS crystal
Tl   0.153800000000000   0.775600000000000   0.114000000000000
Tl   0.224400000000000   0.846200000000000   0.386000000000000
Tl   0.846200000000000   0.224400000000000   0.886000000000000
Tl   0.775600000000000   0.153800000000000   0.614000000000000
Tl   0.222100000000000   0.346700000000000   0.386400000000000
Tl   0.653300000000000   0.777900000000000   0.113600000000000
Tl   0.777900000000000   0.653300000000000   0.613600000000000
Tl   0.346700000000000   0.222100000000000   0.886400000000000
Se   0.946000000000000   0.054000000000000   0.250000000000000
Se   0.054000000000000   0.946000000000000   0.750000000000000
Se   0.426000000000000   0.574000000000000   0.250000000000000
Se   0.574000000000000   0.426000000000000   0.750000000000000
Se   0.145000000000000   0.269000000000000   0.071000000000000
Se   0.731000000000000   0.855000000000000   0.429000000000000
Se   0.855000000000000   0.731000000000000   0.929000000000000
Se   0.269000000000000   0.145000000000000   0.571000000000000
Se   0.952000000000000   0.572000000000000   0.252000000000000
Se   0.428000000000000   0.048000000000000   0.248000000000000
Se   0.048000000000000   0.428000000000000   0.748000000000000
Se   0.572000000000000   0.952000000000000   0.752000000000000
Se   0.736000000000000   0.360000000000000   0.438000000000000
Se   0.640000000000000   0.264000000000000   0.062000000000000
Se   0.264000000000000   0.640000000000000   0.562000000000000
Se   0.360000000000000   0.736000000000000   0.938000000000000
Ga   0.909000000000000   0.291000000000000   0.162000000000000
Ga   0.709000000000000   0.091000000000000   0.338000000000000
Ga   0.091000000000000   0.709000000000000   0.838000000000000
Ga   0.291000000000000   0.909000000000000   0.662000000000000
Ga   0.707000000000000   0.583000000000000   0.339000000000000
Ga   0.417000000000000   0.293000000000000   0.161000000000000
Ga   0.293000000000000   0.417000000000000   0.661000000000000
Ga   0.583000000000000   0.707000000000000   0.839000000000000
K_POINTS automatic
2 2 1 1 1 1
The primitive cell has been created by cif2cell code using the cif file as following:
_journal_issue                   12
_journal_name_full               'Chemistry of Materials'

_journal_page_first              3120
_journal_volume                  23
_journal_year                    2011
_chemical_formula_structural     'Tl Ga Se2'
_chemical_formula_sum            'Ga Se2 Tl'
_chemical_name_systematic        'Thallium Gallium Selenide'
_space_group_IT_number           15
_symmetry_Int_Tables_number      15
_symmetry_space_group_name_Hall  '-C 2yc'
_symmetry_space_group_name_H-M   'C 1 2/c 1'
_audit_creation_date             2008/02/01
_cell_angle_alpha                90.
_cell_angle_beta                 99.993(6)
_cell_angle_gamma                90.
_cell_formula_units_Z            16
_cell_length_a                   10.779(2)
_cell_length_b                   10.776(1)
_cell_length_c                   15.663(5)
_cell_volume                     1791.7(7)
_refine_ls_R_factor_all          0.0652
_[local]_cod_data_source_file    cm200946y_si_002.cif
_[local]_cod_data_source_block   157752-ICSD
_[local]_cod_chemical_formula_sum_orig 'Ga1 Se2 Tl1'
_cod_original_cell_volume        1791.73
_cod_database_code               4000782
loop_
_symmetry_equiv_pos_site_id
_symmetry_equiv_pos_as_xyz
1 'x, -y, z+1/2'
2 '-x, -y, -z'
3 '-x, y, -z+1/2'
4 'x, y, z'
5 'x+1/2, -y+1/2, z+1/2'
6 '-x+1/2, -y+1/2, -z'
7 '-x+1/2, y+1/2, -z+1/2'
8 'x+1/2, y+1/2, z'
loop_
_atom_site_aniso_label
_atom_site_aniso_type_symbol
_atom_site_aniso_U_11
_atom_site_aniso_U_22
_atom_site_aniso_U_33
_atom_site_aniso_U_12
_atom_site_aniso_U_13
_atom_site_aniso_U_23
Tl1 Tl1+ 0.052(6) 0.063(5) 0.06(2) -0.022(3) 0.005(8) 0.000(5)
Tl2 Tl1+ 0.044(6) 0.044(6) 0.07(2) -0.022(3) 0.005(8) 0.002(5)
Ga1 Ga3+ 0.015(9) 0.001(6) 0.05(3) 0.009(6) 0.01(2) -0.019(9)
Ga2 Ga3+ 0.019(7) 0.037(9) 0.00(3) -0.008(9) -0.01(1) -0.01(1)
Se1 Se2- 0.03(1) 0.02(1) 0.06(5) 0. 0.02(2) 0.
Se2 Se2- 0.006(9) 0.001(7) 0.06(4) 0. -0.01(2) 0.
Se3 Se2- 0.04(1) 0.05(1) 0.01(4) 0.01(1) -0.01(2) -0.02(1)
Se4 Se2- 0.012(6) 0.021(7) 0.06(4) 0.01(1) -0.018(9) -0.018(5)
Se5 Se2- 0.05(1) 0.06(1) 0.00(4) -0.053(9) -0.01(2) -0.02(1)
loop_
_atom_site_label
_atom_site_type_symbol
_atom_site_symmetry_multiplicity
_atom_site_Wyckoff_symbol
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_occupancy
_atom_site_attached_hydrogens
Tl1 Tl1+ 8 f 0.4647(6) 0.3109(5) 0.1140(9) 1. 0
Tl2 Tl1+ 8 f 0.2844(4) 0.0623(5) 0.3864(8) 1. 0
Ga1 Ga3+ 8 f 0.100(1) 0.191(2) 0.162(2) 1. 0
Ga2 Ga3+ 8 f 0.145(1) 0.438(1) 0.339(2) 1. 0
Se1 Se2- 4 e 0. 0.054(2) 0.250 1. 0
Se2 Se2- 4 e 0. 0.574(1) 0.250 1. 0
Se3 Se2- 8 f 0.207(1) 0.062(1) 0.071(2) 1. 0
Se4 Se2- 8 f 0.262(1) 0.310(1) 0.252(2) 1. 0
Se5 Se2- 8 f 0.048(2) 0.312(1) 0.438(3) 1. 0
loop_
_atom_type_symbol
_atom_type_oxidation_number
Ga3+ 3
Se2- -2
Tl1+ 1
loop_
_citation_id
_citation_year
_citation_page_first
_citation_page_last
primary 2007 663 666
Are there something wrong in my input file or primitive cell?
With my best wishes,
Mutlu.

------------------------------------------Dr. Mutlu COLAKOGULLARITrakya Universitesi Fen FakultesiFizik Bolumu22030 Merkez-EDİRNE
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