The Vienna Ab initio Simulation Package (VASP) is one of the most widely used software packages for performing first-principles calculations based on Density Functional Theory (DFT). This tutorial provides a practical, step-by-step guide to calculating electronic properties such as band structure and density of states (DOS) using VASP.
Prerequisites
Before starting, you should have:
- Basic understanding of Density Functional Theory
- Access to a Linux-based system or HPC cluster with VASP installed
- Familiarity with terminal commands and text editors
Overview of Electronic Structure Calculations
Electronic structure calculations aim to determine how electrons are distributed in a material. Key quantities obtained from VASP include:
- Band structure
- Total and projected density of states (DOS/PDOS)
- Fermi energy
- Charge density
Required Input Files
A standard VASP calculation requires four main input files:
- POSCAR – crystal structure
- POTCAR – pseudopotentials
- INCAR – calculation parameters
- KPOINTS – Brillouin-zone sampling
Step 1: Preparing the Structure (POSCAR)
The POSCAR file defines the lattice vectors and atomic positions. Always ensure that the structure is fully relaxed before performing electronic calculations.
Step 2: Choosing Pseudopotentials (POTCAR)
Use PAW pseudopotentials supplied with VASP. Consistency between pseudopotentials and exchange-correlation functionals is critical.
Step 3: INCAR Settings for Electronic Properties
Below is a minimal INCAR for a self-consistent field (SCF) calculation:
SYSTEM = SCF Calculation ENCUT = 520 EDIFF = 1E-6 ISMEAR = 0 SIGMA = 0.05 IBRION = -1 NSW = 0 LREAL = Auto
Key parameters:
- ENCUT: Plane-wave cutoff energy
- EDIFF: Electronic convergence criterion
- ISMEAR: Smearing method
Step 4: K-point Sampling
Dense k-point meshes are essential for accurate electronic properties. A typical KPOINTS file for SCF calculations:
Automatic mesh 0 Gamma 8 8 8 0 0 0
Step 5: Self-Consistent Calculation
Run the SCF calculation first to obtain a converged charge density. Always check:
- Energy convergence
- Forces close to zero
- No numerical instabilities
Step 6: Band Structure Calculation
Band structure calculations are non-self-consistent and use a fixed charge density from the SCF run. Update the INCAR:
ICHARG = 11 LWAVE = .FALSE. LCHARG = .FALSE.
The KPOINTS file should follow a high-symmetry path in the Brillouin zone.
Step 7: Density of States (DOS)
For DOS calculations, increase k-point density and enable DOS output:
LORBIT = 11 NEDOS = 2000
The resulting DOSCAR and PROCAR files can be post-processed using tools such as p4vasp, sumo, or pymatgen.
Best Practices
- Always perform convergence tests for ENCUT and k-points
- Use consistent parameters across comparative studies
- Document all input settings for reproducibility
- Validate results with literature or experimental data
Common Pitfalls
- Insufficient k-point sampling
- Using unrelaxed structures
- Incorrect smearing for insulators
- Ignoring symmetry issues
Performance and Efficiency Tips
For large systems, computational efficiency becomes critical:
- Use parallelization over k-points
- Optimize NCORE and KPAR
- Start from well-converged charge densities
Conclusion
VASP provides a powerful and reliable framework for electronic structure calculations. By carefully preparing inputs and following best practices, highly accurate electronic properties can be obtained for a wide range of materials.
This tutorial serves as a practical starting point. In future posts, we will explore advanced topics such as spin–orbit coupling, hybrid functionals, and topological properties using VASP.