Effective masses along two directions are highly anisotropic for a isotropic 2D sheet of GaS. Also the fractional coordinates are not zero for other axis.

[ashima29R]

For GaS 2D monolayer (INPCAR file)
-0.1839 0.3678 0.0000 ! K-POINT in the reciprocal crystal coord. (3 floats)
0.001 ! step size in 1/Bohr units (1 float)
36 ! band number, (1 integer)
V
3.640527884 -6.305579262 0.000000000
3.640527884 6.305579262 0.000000000
0.000000000 0.000000000 16.393389123 ! program identifier (1)

the vasp output:
Effective mass (0): -2.029
Original eigenvectors: 0.00000 0.00000 0.00000
Normal fractional coordinates: -0.03064 1.00000 0.00335

Effective mass (1): -13.022
Original eigenvectors: 0.00000 0.00000 0.00000
Normal fractional coordinates: 1.00000 0.52286 -0.01380

~

[VincentVandalon]

@ashima29R Did you ever resolve this issue? We are having similar problems with MoS2, where it appears that one of the two in plane-effective masses is swapped for the out-of-plane effective mass.

[afonari]

What is the 'expected' output?

[VincentVandalon]

For the electrons at the T point (direction) of MoS2 we expect:

• effective mass in-plane1 == effective mass in-plane2 (in-plane -> with k vector in xy plane)
• A much higher out of plane mass (k vector in z direction)

But we find:

• effective mass in-plane1 == effective mass out-of-plane
• effective mass in-plane-2 >>> effective mass in-plane1

The weird thing is, this does not happen for other k-points. Using VASP by the way.

[ashima29R]

Dear Sir; Greeting from India!! The effective mass for GaS is coming out to be highly anisotropic whereas the effective mass for InSe which is similar in physical struture and bandstructure to GaS is reported to be highly isotropic (*Nanoscale*, 2017, *9*, 14682-146089). Also I have tried using emc for InSe but it give very highly anisotopic values in x and y directions. This was not an issue with MoS2 ans WS2 which I have calculated earlier , the masses along x and y direction were coming out to be isotropic Thanking You; With Regards; Ashima Rawat