Opening this thread for discussion on features for treatment of wavefunctions files, focusing on VASP WAVECARs for now.

Integrating some of our existing tools into httk would increase postprocessing capabilities of workflows and provide useful functionality not generally supported by other packages. Writing new WAVECARs could enable direct manipulation of wavefunctions between calculations or more sparse storage of only vital wavefunction information.

Features

This extension should at its core enable:

• Opening a WAVECAR file without loading it all into memory, including contained eigenvalue and occupation information
• Extracting planewave coefficients of specific band at k-point and spin channel
• Extracting a realspace-transformed wavefunctions from coefficients or indices
• Writing a WAVECAR, or a subselection of WAVECAR data, into a new file

It may optionally support:

• Opening a gamma-version WAVECAR and supporting above points
• Possibility of writing to both standard and gamma-format, when applicable
• Support writing of wavefunctions to easily visualizable file formats (e.g., VESTA)
• Extendability to other planewave-based wavefunction file formats (e.g., QuantumEspresso).
• Spin-orbit-coupling format WAVECARs