Among the optical properties obtainable from absorbance measurement, the absorption coefficient can obtain by calculating the dielectric function and refractive index. When the real parts and imaginary parts of the dielectric function are called ε1 and ε2, and expressed as a function of the refractive index are as follows.
In here, the n(ω) and k(ω) are the real part and imaginary part of the refractive index.
Also, the function of the absorption coefficient (α) and the refractive index is defined as follows. In general, units of cm-1 are often used.
Therefore, we can obtain the absorption coefficient and the refractive index of material from dielectric function calculation.
The absorption coefficient is particularly important in the semiconductor field. For example, perovskite solar cells have improved conversion efficiency as around 23 % than the conventional solar cell. In this case, the increased absorption coefficient can be used as an indicator of efficiency improvement.
It can also be applied to the quantum dot TV, which is a promising technique recently. There is a problem that the light efficiency becomes lower due to the interaction between quantum dots. It can be solved using analyzing the absorption coefficient or optical extraction efficiency.
Recently, the 'Optical property' option has been updated in the Quantum Espresso module.
You can calculate the optical properties of materials with a few clicks.
We'll learn about how to calculate the dielectric function, refractive index, and the absorption coefficient of material in this module tip, with example video.
Optical Property Calculation Procedure
Optical Property Calculation
1. Modeling the structure.
2. Perform relaxation calculation.
3. Load the optimized structure to the structure builder.
4. Perform the SCF calculation.
If you select the ‘Optical property’ option of ‘Data to get,’ the input script changed automatically to be fit to calculate the optical property.
‘noinv = .TRUE.’
‘nosym = .TRUE.’
Pseudopotential type: NC
5. After the calculation finishes, click the ‘Update Status’ button.
Optical Property Post-processing Calculation
6. Perform the NSCF calculation.
If you select the ‘Optical property (restart)’ option of ‘Data to get,’ the input script changed automatically to be fit to calculate the optical property.
‘Optical property’ tab added
‘Calculation type = ‘nscf’’
k-points grid increased
7. You can modify the input script for the optical property post-processing calculation on the ‘Optical property’ tab. And also, click the + button of the right to add more ‘Optical property’ tab.
8. After the calculation finishes, click the ‘Update Status’ button.
9. Add the ‘Optical Property’ module.
10. Connect that to the 'Quantum Espresso' module having ‘Optical property’ post-processing tab.
Do you need more information?
[Modules] Quantum Espresso
[Appendix] To Learn about Quantum Espresso inputs
#15 How to Decide the Optimal Electronic/Atomic Structure Using a Computer: Relaxation (2) – Structural Relaxation
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