Units And Interoperability

kMCpy uses fixed internal unit conventions. Keep these units explicit when building models or connecting external codes.

Unit Table

Quantity	Unit
Migration barrier and fitted energy terms	meV
Site-energy difference returned to kMCpy	meV
Event rate and attempt frequency	Hz
Temperature	K
Simulation time	s
Length, displacement, elementary hop distance	Angstrom
Volume	Angstrom^3
Mean squared displacement	Angstrom^2
Jump and tracer diffusivity	cm^2/s
Conductivity	mS/cm
Mobile ion charge	`
Haven ratio and correlation factor	dimensionless

In code:

from kmcpy import Configuration

print(Configuration.field_units())
print(tracker.result_units)

Model Units

LocalBarrierModel barriers are in meV.

LocalClusterExpansion fitted targets are in meV. If the LCE is used as a kra_model, the fitted target is E_KRA. If it is used as a site_model, the fitted target is the site-energy-difference contribution expected by the composite model.

SiteEnergyModel can accept external values in eV or meV through its units argument and converts them to meV for kMCpy.

Differences From Other Codes

Other atomistic software often has a different primary purpose:

• smol, CLEASE, and CASM are commonly used for cluster expansion and Monte Carlo workflows on configurational lattices.

• ASE is a general atomistic structure and calculator interface.

• kMCpy focuses on event-based kinetic Monte Carlo for migration on an active-site network.

When connecting these tools, the important question is not just “can both codes store an occupation?” It is whether they agree on:

• site order,

• species or state encoding,

• units,

• whether an energy is absolute or a local event difference,

• how an accepted kMC event updates the external runtime state.

For site-energy-difference adapters, kMCpy precomputes site and state mappings once before the run. During the kMC loop, it passes only the changed endpoints to the external callable.

See Use site-energy-difference models for mapped external-code examples.