ediff

EDIFF is a convergence parameter used in many first-principles electronic structure calculations, most prominently in density functional theory workflows. It specifies the allowable difference in the calculated electronic energy between successive self-consistent field (SCF) iterations. In practice, the SCF loop repeats until the absolute change in total energy from one electronic step to the next falls below the EDIFF value, at which point the electronic structure is considered converged.

The EDIFF criterion is separate from other convergence controls such as ionic relaxation. A smaller EDIFF generally yields more tightly converged electronic results but requires more SCF iterations and longer compute times. In contrast, a larger EDIFF speeds up calculations but may introduce a slight loss of electronic accuracy. Many codes also provide related parameters (for example, EDIFFG in some packages) to govern convergence criteria for other parts of the calculation, such as ionic steps driven by forces.

Typical values for EDIFF are in the range of 1e-5 to 1e-6 eV for standard calculations, with tighter values (e.g., 1e-7 eV) used for high-precision work. Default settings vary by code and system; researchers often start with a moderate value and adjust based on convergence behavior and the sensitivity of results to electronic energy.

Because the exact implementation of EDIFF can differ slightly between software packages, users should consult the documentation for their specific code to confirm how EDIFF is defined and applied and how it interacts with other convergence controls.