What are pseudopotentials and PAW?

Pseudopotentials and the Projector Augmented Wave (PAW) method are techniques for simplifying DFT calculations by replacing the deep core electrons with an effective potential.

Why Pseudopotentials Are Used

Core electrons (1s, 2s, 2p for heavy elements) are tightly bound and do not participate in chemical bonding. Including them explicitly requires very fine numerical grids and many basis functions, making calculations prohibitively expensive.

Pseudopotential Approach

A pseudopotential replaces the true all-electron potential near the nucleus with a smoother effective potential that:

1. Reproduces the correct scattering properties for valence electrons
2. Gives the same eigenvalues as the all-electron calculation outside a cutoff radius
3. Allows much lower plane-wave energy cutoffs (300-600 eV vs. thousands of eV)

PAW Method

The Projector Augmented Wave (PAW) method, used by VASP and other codes, is a more rigorous formalism that:

• Maintains the full all-electron wavefunction information
• Provides better total energies and forces than norm-conserving pseudopotentials
• Is the standard in Materials Project and AFLOW calculations

Practical Impact

Different pseudopotential libraries can give slightly different property values. This is one reason why the same material may have different computed properties in different databases.