name: optical-properties
description: Optical Properties Calculations (6 sub-skills: absorption-spectrum, dielectric-function, joint-dos, optical-conductivity, slme, transition-dipole)
Optical Properties Calculations
Overview
This skill group covers the calculation of optical properties from first principles using Quantum ESPRESSO. The central quantity is the frequency-dependent dielectric function, from which all other optical properties (absorption coefficient, reflectivity, refractive index, optical conductivity) are derived.
The workflow always begins with a well-converged SCF calculation followed by QE's epsilon.x post-processing tool, which computes the dielectric function within the Random Phase Approximation (RPA) / independent-particle approximation.
MACE cannot compute optical properties. Optical response requires electronic wavefunctions and transition matrix elements, which are only available from DFT. MACE can be used to pre-relax the structure before a QE calculation.
Sub-Skills
| Sub-Skill |
Directory |
Description |
| Dielectric Function |
dielectric-function/ |
Frequency-dependent dielectric function (real and imaginary parts), static dielectric constant, Born effective charges |
| Absorption Spectrum |
absorption-spectrum/ |
Optical absorption coefficient, joint density of states, reflectivity, refractive index vs photon energy |
| Optical Conductivity |
optical-conductivity/ |
Frequency-dependent optical conductivity from dielectric function, Drude model for metals, sum rules |
Method Decision Guide
Need optical properties of a material?
|
+--> Step 1: Relax structure (MACE quick relax or QE vc-relax)
|
+--> Step 2: QE SCF with dense k-grid and many empty bands
|
+--> Step 3: epsilon.x to compute dielectric function
|
+--> Step 4: Post-process to desired property
|
+--> Dielectric function? --> dielectric-function/ skill
|
+--> Absorption, reflectivity, refractive index? --> absorption-spectrum/ skill
|
+--> Optical conductivity? --> optical-conductivity/ skill
Common Prerequisites
- Pseudopotentials: QE calculations require pseudopotential files. All sub-skills show how to download SSSP pseudopotentials automatically.
- Structure files: Start from a CIF, POSCAR, or build with pymatgen/ASE.
- Dense k-grid: Optical properties converge slowly with k-point density. Use at least 12x12x12 for bulk, denser for small-gap systems.
- Many empty bands:
nbnd must be large enough to capture transitions up to the desired photon energy. Typically 2--4x the number of occupied bands.
- Python environment: pymatgen, ASE, numpy, scipy, matplotlib are pre-installed.
- QE executables:
pw.x, epsilon.x, ph.x (for Born charges).
Important Notes
- QE
epsilon.x computes the independent-particle (RPA) dielectric function. It does not include excitonic effects (use BSE/GW for that, not available in standard QE).
- PBE underestimates band gaps, which shifts optical absorption onset to lower energies. Use scissors correction (
intersmear broadening can partially compensate but does not fix the gap).
- For metals, the intraband (Drude) contribution must be added separately -- see the optical-conductivity skill.
- All optical property sub-skills share the same SCF + epsilon.x foundation. Run SCF once, then derive multiple properties from the same epsilon.x output.
1---2name: optical-properties3description: This skill group covers the calculation of optical properties from first principles using Quantum ESPRESSO. The central quantity is the frequency-dependent dielectric function, from which all other optical properties (absorption coefficient, reflectivity, refractive index, optical conductivity) are derived.4---5
6---
7name: optical-properties
8description: Optical Properties Calculations (6 sub-skills: absorption-spectrum, dielectric-function, joint-dos, optical-conductivity, slme, transition-dipole)
9---
10
11# Optical Properties Calculations
12
13## Overview
14
15This skill group covers the calculation of optical properties from first principles using Quantum ESPRESSO. The central quantity is the frequency-dependent dielectric function, from which all other optical properties (absorption coefficient, reflectivity, refractive index, optical conductivity) are derived.
16
17The workflow always begins with a well-converged SCF calculation followed by QE's `epsilon.x` post-processing tool, which computes the dielectric function within the Random Phase Approximation (RPA) / independent-particle approximation.
18
19**MACE cannot compute optical properties.** Optical response requires electronic wavefunctions and transition matrix elements, which are only available from DFT. MACE can be used to pre-relax the structure before a QE calculation.
20
21## Sub-Skills
22
23| Sub-Skill | Directory | Description |
24|---|---|---|
25| Dielectric Function | `dielectric-function/` | Frequency-dependent dielectric function (real and imaginary parts), static dielectric constant, Born effective charges |
26| Absorption Spectrum | `absorption-spectrum/` | Optical absorption coefficient, joint density of states, reflectivity, refractive index vs photon energy |
27| Optical Conductivity | `optical-conductivity/` | Frequency-dependent optical conductivity from dielectric function, Drude model for metals, sum rules |
28
29## Method Decision Guide
30
31```
32Need optical properties of a material?
33 |
34 +--> Step 1: Relax structure (MACE quick relax or QE vc-relax)
35 |
36 +--> Step 2: QE SCF with dense k-grid and many empty bands
37 |
38 +--> Step 3: epsilon.x to compute dielectric function
39 |
40 +--> Step 4: Post-process to desired property
41 |
42 +--> Dielectric function? --> dielectric-function/ skill
43 |
44 +--> Absorption, reflectivity, refractive index? --> absorption-spectrum/ skill
45 |
46 +--> Optical conductivity? --> optical-conductivity/ skill
47```
48
49## Common Prerequisites
50
51- **Pseudopotentials**: QE calculations require pseudopotential files. All sub-skills show how to download SSSP pseudopotentials automatically.
52- **Structure files**: Start from a CIF, POSCAR, or build with pymatgen/ASE.
53- **Dense k-grid**: Optical properties converge slowly with k-point density. Use at least 12x12x12 for bulk, denser for small-gap systems.
54- **Many empty bands**: `nbnd` must be large enough to capture transitions up to the desired photon energy. Typically 2--4x the number of occupied bands.
55- **Python environment**: pymatgen, ASE, numpy, scipy, matplotlib are pre-installed.
56- **QE executables**: `pw.x`, `epsilon.x`, `ph.x` (for Born charges).
57
58## Important Notes
59
60- QE `epsilon.x` computes the **independent-particle** (RPA) dielectric function. It does not include excitonic effects (use BSE/GW for that, not available in standard QE).
61- PBE underestimates band gaps, which shifts optical absorption onset to lower energies. Use scissors correction (`intersmear` broadening can partially compensate but does not fix the gap).
62- For metals, the intraband (Drude) contribution must be added separately -- see the optical-conductivity skill.
63- All optical property sub-skills share the same SCF + epsilon.x foundation. Run SCF once, then derive multiple properties from the same epsilon.x output.
majiayu000