Reading and writing VASP WAVECAR files

httk-atomistic provides the numpy-backed binary WAVECAR layer through httk.atomistic.integrations.vasp.io. It reads the small metadata headers eagerly and reads one coefficient vector at a time, which keeps the large coefficient data on disk until requested. This is the low-level binary reader/writer; for the domain-level PlaneWaveFunctions object built on top of it, see Plane-wave wavefunctions.

Installation and dispatch

WAVECAR support requires the optional numpy extra:

python -m pip install -e '.[numpy]'

Importing httk.core discovers the WAVECAR reader and writer (registered through httk.registry.io.atomistic). Files named WAVECAR and files with the .wavecar extension are registered. The core loader returns a neutral payload:

import httk.core

payload = httk.core.load("WAVECAR", raw=True)
assert payload["format"] == "vasp-wavecar"
source = payload["wavecar"]

The wavecar value is a WavecarSource contract, not an atomistic-domain object. It exposes nspins, nkpts, nbands, encut, cell, kpoints, eigenvalues, occupations, nplanewaves, double_precision, and coefficients(spin, kpt, band). record_length is specific to an open WavecarFile and is not part of the common source contract. The atomistic layer can provide the same contract for in-memory data without depending on the concrete WavecarFile class.

All indices are zero-based:

coefficients = source.coefficients(spin=0, kpt=0, band=0)

WavecarFile is also a context manager. Its metadata arrays have shapes (nkpts, 3), (nspins, nkpts, nbands), and (nkpts,) for k-points, eigenvalues/occupations, and plane-wave counts respectively.

Compression and writing

WAVECAR is a random-access binary format. Compressed paths are deliberately refused: streaming decompression cannot support seeking to arbitrary spin/k-point/band coefficient records. Decompress a file on disk before reading it. Writing likewise requires a binary filesystem path rather than a compressed or text stream.

from httk.atomistic.integrations.vasp.io import read_wavecar, write_wavecar

payload = read_wavecar("WAVECAR")
write_wavecar("WAVECAR.copy", payload)

write_wavecar accepts the neutral vasp-wavecar payload and any source that implements the WavecarSource contract. It preserves single- versus double-precision coefficient storage according to double_precision.

VASP/VESTA volumetric output

write_vasp_volumetric writes POSCAR content followed by a three-dimensional, real-valued grid in Fortran order. It is the low-level writer used when a wavefunction or other scalar field needs to be opened by VESTA; pass grid.real or grid.imag explicitly for a complex array.

from httk.atomistic.integrations.vasp.io import write_vasp_volumetric

write_vasp_volumetric("wave_r.vasp", poscar_payload, wave.real)
write_vasp_volumetric("wave_i.vasp", poscar_payload, wave.imag)