Calculations are done using VASP software. Convergence on KPOINTS and ENCUT is done with respect to total energy of the system within 0.001 eV tolerance. Please note convergence on KPOINTS and ENCUT is generally done for target properties, but here we assume energy-convergence with 0.001 eV should be sufficient for other properties also. The points on the curves are obtained with single-point calculation (nuber of ionic steps,NSW=1). However, for very accurate calculations, NSW>1 might be needed.
The following shows the X-ray diffraction (XRD) pattern and the Radial distribution function (RDF) plots.
The following shows the electronic density of states and bandstructure. DFT is generally predicted to underestimate bandgap of materials. Accurate band-gaps are obtained with higher level methods (with high computational requirement) such as HSE, GW, which are under progress. Total DOS, Orbital DOS and Element dos buttons are provided for density of states options. Energy is rescaled to make Fermi-energy zero. In the bandstructure plot, spin up is is shown with blue lines while spin down are shown with red lines. Non-degenerate spin-up and spin-down states (if applicable) would imply a net orbital magnetic moment in the system.
Bandgap (eV): 2.119 I
The following plot shows the plane averaged electrostatic potential (ionic+Hartree) along z direction. The red line shows the Fermi-energy while the green line shows the maximum value of the electrostatic potential. For slab structures (with vacuum along z-direction), the difference in these two values can be used to calculate work-function of the material.
Incident photon energy dependence of optical is shown below. Only interband optical transitions are taken into account.Please note the underestimatation of band-gap problem with DFT will reflect in the spectra as well. For very accurate optical properties GW/BSE calculation would be needed, which is yet to be done because of their very high computational cost. Optical properties for layered materials needs to be rescaled with the actual thickness to simulation z-box ratio. Absorption coeffiecient is in cm-1 unit.
Elastic tensor calculated for the conventional cell of the system with finite-difference method. For layered materials, the elastic constants are rescaled with respect to vacuum padding (see the input files) and the units for elastic coefficients are in N/m. Phonons obtained from this calcuation are also shown.
WARNING: Please note this may not be the exact phonon modes of the system as we did not test the cell-size dependence of phonons yet. At least 1.2 nm x1.2 nm x1.2 nm or more is needed for obtaining reliable phonon spectrum. For systems having primitive-cell phonon representation tables, I denotes infrared activity and R denotes Raman active modes (where applicabale).
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|
|||||
|---|---|---|---|---|---|
| 0.5 | 0.0 | -0.0 | 0.0 | 0.0 | 0.0 |
| 0.0 | 0.5 | -0.0 | 0.0 | 0.0 | 0.0 |
| -0.0 | -0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 0.0 | 0.0 | 0.0 | 0.2 | 0.0 | 0.0 |
| 0.0 | 0.0 | 0.0 | 0.0 | -1.9 | 0.0 |
| 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | -1.9 |
| Phonon mode (cm-1) |
|---|
| -84.9284721927 |
| -84.9284561826 |
| -0.7255295501 |
| -0.7251208944 |
| -0.2586200991 |
| 105.047735604 |
| 105.047745726 |
| 737.247290937 |
| 854.853715006 |
point_group_type: 6/mmm
| Phonon mode (cm-1) | Visualize Phonons hereRepresentation |
|---|---|
| -84.9284721927 | E1g R |
| -0.7255295501 | E1u I |
| -0.2586200989 | A2u I |
| 105.047735604 | E1u I |
| 737.247290937 | A1g R |
| 854.853715006 | A2u I |
Thermoelectric properties are calculated using BoltzTrap code. Electron and hole mass tensors are given at 300 K. Following plots show the Seebeck coefficient and ZT factor (eigenvalues of the tensor shown) at 300 K along three different crystallographic directions. Seebeck coefficient and ZT plots can be compared for three different temperatures available through the buttons given below. Generally very high Kpoints are needed for obtaining thermoelectric properties. We assume the Kpoints obtained from above convergence were sufficient.
WARNING: Constant relaxation time approximation (10-14 s) and only electronic contribution to thermal conductivity were utilized for calculating ZT.
| 2.13144157106 | -1.23818223793e-16 | -7.23360316921e-16 |
| -1.23818223793e-16 | 2.13144431178 | -6.40430981738e-18 |
| -7.23360316921e-16 | -6.40430981738e-18 | 2677.13379303 |
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|
||
|---|---|---|
| 33.0994314707 | -1.0503183716e-15 | -3.50654708e-16 |
| -1.0503183716e-15 | 33.0994738483 | -4.17046825518e-18 |
| -3.50654708e-16 | -4.17046825518e-18 | 18834.8199566 |