Calculating the thermoelectric properties of 2D materials using VASP involves multiple steps, including structural relaxation, electronic structure calculations, and transport properties evaluation using a post-processing tool like BoltzTraP2. Below is a detailed guide on the steps and important INCAR tags for each stage.

### Step 1: Structural Optimization

#### 1.1 POSCAR

Ensure your POSCAR file accurately represents your 2D material structure.

#### 1.2 INCAR for Structural Optimization

Use the following key tags in the INCAR file:

```plaintext

SYSTEM = Your_2D_Material_Name

# Electronic Relaxation

ENCUT = 500 # Plane-wave cutoff energy (adjust as needed)

PREC = Accurate # Precision mode

EDIFF = 1E-6 # Convergence criterion for electronic steps

# Ionic Relaxation

ISIF = 3 # Relaxation of ions and cell shape/volume

IBRION = 2 # Algorithm for ionic relaxation (conjugate gradient)

NSW = 100 # Maximum number of ionic steps

EDIFFG = -0.01 # Convergence criterion for ionic steps (force convergence in eV/Å)

# 2D Material Specifics

LREAL = Auto # Projector-augmented wave (PAW) method

GGA = PE # Exchange-correlation functional

```

#### 1.3 KPOINTS

Use a dense k-point grid for accurate results, e.g., 15x15x1.

#### 1.4 POTCAR

Ensure you have the appropriate POTCAR files for your elements.

### Step 2: Static Electronic Structure Calculation

#### 2.1 INCAR for Static Calculation

After structural optimization, perform a static electronic structure calculation:

```plaintext

SYSTEM = Your_2D_Material_Name_Static

# Electronic Relaxation

ENCUT = 500

PREC = Accurate

EDIFF = 1E-8 # Tight electronic convergence criterion

# Static Calculation Specifics

ISTART = 0 # Job starting mode

ICHARG = 11 # Charge density from the previous run

LORBIT = 11 # Orbital projection

ISMEAR = 0 # Gaussian smearing

SIGMA = 0.05 # Smearing width in eV

LWAVE = .TRUE. # Write WAVECAR

LCHARG = .TRUE. # Write CHGCAR

```

#### 2.2 KPOINTS

Use the same dense k-point grid (15x15x1) for consistency.

### Step 3: Density of States (DOS) and Band Structure Calculations

#### 3.1 INCAR for DOS Calculation

```plaintext

SYSTEM = Your_2D_Material_Name_DOS

# Electronic Relaxation

ENCUT = 500

PREC = Accurate

EDIFF = 1E-8

# DOS Calculation Specifics

ICHARG = 11

LORBIT = 11

ISMEAR = 0

SIGMA = 0.05

LWAVE = .TRUE.

LCHARG = .TRUE.

NEDOS = 2000 # Number of DOS points

```

#### 3.2 KPOINTS for DOS

Use a denser k-point mesh for DOS, e.g., 30x30x1.

#### 3.3 INCAR for Band Structure Calculation

```plaintext

SYSTEM = Your_2D_Material_Name_Band

# Electronic Relaxation

ENCUT = 500

PREC = Accurate

EDIFF = 1E-8

# Band Structure Specifics

ICHARG = 11

LORBIT = 11

ISMEAR = 0

SIGMA = 0.05

LWAVE = .TRUE.

LCHARG = .TRUE.

```

#### 3.4 KPOINTS for Band Structure

Specify the high-symmetry points in the reciprocal lattice:

```plaintext

Line-mode

reciprocal

12

0.0 0.0 0.0 ! Gamma

0.5 0.0 0.0 ! M

...

```

### Step 4: Transport Properties Calculation Using BoltzTraP2

#### 4.1 Generate BoltzTraP2 Input Files

1. **Run VASP to produce WAVECAR and CHGCAR files.**

2. **Convert VASP output to BoltzTraP2 input format using `vasp2boltz.py` script** (make sure you have the script).

#### 4.2 BoltzTraP2 Calculation

```shell

boltztrap2 -f vasp

```

Configure BoltzTraP2 parameters, typically in a `boltztrap2.def` file, as needed for your specific system and the properties you wish to calculate.

### Important Notes:

- **Accuracy:** Ensure high accuracy in all calculations, especially for electronic structure calculations, to obtain reliable transport properties.

- **k-point Density:** A dense k-point mesh is crucial for accurate band structure and DOS calculations, affecting the accuracy of transport properties.

- **Convergence Tests:** Perform convergence tests for cutoff energy (ENCUT), k-point mesh, and other parameters to ensure the reliability of your results.

By following these steps, you should be able to calculate the thermoelectric properties of 2D materials using VASP and BoltzTraP2.