Input Structures and findinter

Input Structures and findinter

findinter builds PAIPAI struc.in files from metal-only POSCAR files.

It is useful when the interstitial candidate sites are not already known, including:

• bulk alloys
• grain boundaries
• slabs
• vacancies and defect structures
• distorted cells

Basic Command

findinter \
  --input POSCAR_metal_only \
  --inter B,O \
  --internum 4,5 \
  --gn 100 \
  --min-void-factor 0.9 \
  --max-void-factor 1.2 \
  --output struc.in \
  --site-poscar interstitial_sites.vasp

radii.dat

radii.dat is an input file for findinter. It supplies the effective hard-sphere radii used to decide where interstitial candidate sites are allowed.

If the file is missing, findinter writes a default template and exits without generating the final struc.in. This is intentional: you should inspect or edit the radii, then rerun the same findinter command.

Example:

# PAIPAI findinter hard-sphere radii in Angstrom
Nb 1.428
Ta 1.428
Ti 1.428
Hf 1.428
Interstitial 0.55

The metal entries are keyed by element symbol. Interstitial is a single effective radius used for the candidate interstitial-site search, even when more than one interstitial species is requested.

These are effective search parameters, not immutable tabulated atomic radii:

• Increasing a metal radius makes the metal atoms exclude more nearby grid points.
• Decreasing the Interstitial radius allows sites closer to each other and closer to metals.
• Increasing the Interstitial radius makes the site search more conservative and suppresses nearby candidate sites more strongly.
• For BCC-like refractory alloys, a smaller Interstitial radius can be useful for recovering tetrahedral candidate sites.

The distance window also depends on --min-void-factor and --max-void-factor, so the effective lower and upper nearest-metal criteria are:

min distance = min_void_factor * (r_metal + r_interstitial)
max distance = max_void_factor * (r_metal + r_interstitial)

Grid Modes

Exactly one grid mode must be used:

Option	Meaning
--gn N	Same grid count along x, y, and z.
--gnx N --gny N --gnz N	Explicit grid counts along each direction.
--gstep X	Derive grid counts from a target Cartesian grid step.

Void Factors

findinter keeps grid points whose nearest-metal distance satisfies:

d_nearest >= min_void_factor * (r_metal + r_interstitial)
d_nearest <= max_void_factor * (r_metal + r_interstitial)

The retained clearance field is searched for local maxima. After selecting one site, nearby grid points are suppressed to avoid duplicate sites.

Output Files

File	Meaning
struc.in	PAIPAI input structure with metal sites and interstitial candidate sites.
interstitial_sites.vasp	Optional visualization POSCAR with candidate sites marked as H atoms.

radii.dat is not a normal output of a successful run. It is an input file; findinter only creates it as a template when the file is missing, then exits so the user can review it.