Overview: Ti₂Se₂

Structure info
Layer group	p4/nmm
Layer group number	64
Structure origin	original03-18
ICSD id of parent bulk structure	ICSD 162897

Stability
Energy above convex hull [eV/atom]	0.298
Heat of formation [eV/atom]	-0.833
Dynamically stable	No

Basic properties
Magnetic	No
Band gap (PBE) [eV]	0.000

Repeat: 1234   Download: XYZ CIF JSON

Axis	x [Å]	y [Å]	z [Å]	Periodic
1	4.160	0.000	0.000	Yes
2	-0.000	4.160	0.000	Yes
3	-0.000	0.000	18.233	No

Lengths [Å]	4.160	4.160	18.233
Angles [°]	90.000	90.000	90.000

Crystal structure

Symmetries
2D Bravais type	Square (tp)
Layer group number	64
Layer group	p4/nmm
Space group number (bulk in AA-stacking)	129
Space group (bulk in AA-stacking)	P4/nmm
Point group	4/mmm
Inversion symmetry	Yes

Structure data
Formula	Ti2Se2
Stoichiometry	AB
Number of atoms	4
Unit cell area [Å2]	17.306
Thickness [Å]	2.895

Stability

Convex hull

Se2Ti2 (2SeTi-2)
Heat of formation [eV/atom]	-0.83
Energy above convex hull [eV/atom]	0.30

Monolayers from C2DB
Ti4Se8 (4TiSe2-1)	-1.13 eV/atom
Ti2Se3 (1Ti2Se3-1)	-1.12 eV/atom
TiSe2 (1TiSe2-1)	-1.12 eV/atom
TiSe2 (1TiSe2-2)	-1.00 eV/atom
Ti2Se2 (2SeTi-1)	-0.87 eV/atom
TiSe2 (1TiSe2-3)	-0.86 eV/atom
Ti2Se2, (2SeTi-2)	-0.83 eV/atom
Ti2Se6 (2TiSe3-1)	-0.83 eV/atom
Ti2Se2 (2SeTi-3)	-0.78 eV/atom
Ti2Se2 (2SeTi-4)	-0.56 eV/atom
Ti2Se2 (2SeTi-5)	-0.55 eV/atom
Se2 (2Se-1)	0.21 eV/atom
Se2 (2Se-2)	0.29 eV/atom

Bulk crystals from OQMD123
Ti6Se8	-1.22 eV/atom
Ti2Se4	-1.12 eV/atom
Ti5Se4	-1.06 eV/atom
Ti24Se12	-0.83 eV/atom
Se3	0.00 eV/atom
Ti3	0.00 eV/atom

Phonons

Minimum eigenvalue of Hessian [eV/Ų]

-0.00

Linear deformations

Stiffness tensor

Cij (N/m)	xx	yy	xy
xx	23.19	32.80	-0.00
yy	32.82	23.20	-0.00
xy	0.00	0.00	33.93

Stiffness tensor eigenvalues
Eigenvalue 0	-9.61 N/m
Eigenvalue 1	33.93 N/m
Eigenvalue 2	56.00 N/m

Electronic bands

Band structure and DOS

Key values [eV]
Band gap (PBE)	0.000
Direct band gap (PBE)	0.000
Fermi level wrt. vacuum (PBE)	-4.237

Fermi surface

Electronic properties

Bader charges

Atom No.	Chemical symbol	Charges [|e|]
0	Ti	1.18
1	Ti	1.18
2	Se	-1.18
3	Se	-1.18

Optical properties

Optical polarizability

Properties
Interband polarizability (x) [Å]	11.672
Interband polarizability (y) [Å]	11.616
Interband polarizability (z) [Å]	0.332
Plasma frequency (x) [eV Å0.5]	6.623
Plasma frequency (y) [eV Å0.5]	6.627

Miscellaneous

Miscellaneous details
Unique ID	2SeTi-2
Number of atoms	4
Number of species	2
Formula	Ti2Se2
Reduced formula	TiSe
Stoichiometry	AB
Unit cell area [Å2]	17.306
Original file-system folder	/home/niflheim2/cmr/C2DB-ASR/tree/AB/SeTi/Se2Ti2-4209d7977c0a
Old uid	Se2Ti2-4209d7977c0a
Space group (bulk in AA-stacking)	P4/nmm
Space group number (bulk in AA-stacking)	129
Point group	4/mmm
Inversion symmetry	Yes
Layer group number	64
Layer group	p4/nmm
2D Bravais type	Square (tp)
Thickness [Å]	2.895
Structure origin	original03-18
Band gap (PBE) [eV]	0.000

Miscellaneous details
Direct band gap (PBE) [eV]	0.000
gap_dir_nosoc	0.000
Vacuum level [eV]	3.095
Fermi level wrt. vacuum (PBE) [eV]	-4.237
minhessianeig	-0.000
Dynamically stable	No
Interband polarizability (x) [Å]	11.672
Interband polarizability (y) [Å]	11.616
Interband polarizability (z) [Å]	0.332
Plasma frequency (x) [eV Å0.5]	6.623
Plasma frequency (y) [eV Å0.5]	6.627
Energy [eV]	-23.677
ICSD id of parent bulk structure	ICSD 162897
Magnetic	No
Spin axis	z
Magnetic anisotropy energy, xz [meV/unit cell]	0.000
Magnetic anisotropy energy, yz [meV/unit cell]	0.000
Energy above convex hull [eV/atom]	0.298
Heat of formation [eV/atom]	-0.833