[EA] Section

Last updated: October 12, 2026

The [EA] section is required when using EA or EA-vc, or when append_struc_ea = True is specified in the [option] section.
See also CrySPY > Search algorithms > EA

EA

Name	Value	Default	Description
`n_pop`	int		Population (see also Population Size)
`n_crsov`	int		Number of offspring created by crossover
`n_perm`	int		Number of offspring created by permutation
`n_strain`	int		Number of offspring created by strain
`n_rand`	int		Number of structures created randomly
`n_elite`	int		Number of elite individuals (see also Natural Selection)
`fit_reverse`	bool	`False`	If `False`, minimal search (see also Evaluate Fitness)
`n_fittest`	int	0	Number of individuals that remain natural selection. If set to 0, all individuals are retained.
`slct_func`	`TNM`, `RLT`		Function to select parents
`t_size`	int	3	Tournament size. Used only used `slct_func = TNM`. (see also Tournament Selection)
`a_rlt`	float	10.0	Parameter for linear scaling. Used only with `slct_func = RLT`. (see also Roulette Selection)
`b_rlt`	float	1.0	Parameter for linear scaling. Used only with `slct_func = RLT`. (see also Roulette Selection)
`crs_lat`	`equal`, `random`	`random`	How to mix lattice vectors (see also crossover > 5. Swap the sliced halves)
`nat_diff_tole`	int	4	Tolerance for difference in the number of atoms in crossover. (see also crossover > 6. Select the offspring with more atoms)
`ntimes`	int	1	Number of times in permutation.
`sigma_st`	float	0.5	Standard deviation for strain.
`maxcnt_ea`	int	50	Maximum number of trials in EA.
`max_parent_attempts`	int	50	(since version 1.5.0) Maximum number of parent-selection attempts per offspring in EA. The initial parent selection is included.
`maxgen_ea`	int	0	Maximum generation. If set to 0, no upper limit is applied.
`emax_ea`	float	`None`	Energy upper limit (eV/atom) for natural selection.
`emin_ea`	float	`None`	Energy lower limit (eV/atom) for natural selection.

EA-vc

EA-vc requires the following additional variables on top of the standard EA.
Note that in EA-vc, emax_ea and emin_ea are used not in natural selection but when computing the convex hull.
See also CrySPY > Search algorithms > EA-vc
See also CrySPY > Tutorial > EA-vc > Analysis and visualization for the convex hull plot.

Name	Value	Default	Description
`n_add`	int		Number of offspring created by addition.
`add_max`	int	5	(since version 1.4.1) Maximum number of atoms to add in addition
`n_elim`	int		Number of offspring created by elimination.
`elim_max`	int	5	(since version 1.4.1) Maximum number of atoms to eliminate in elimination
`n_subs`	int		Number of offspring created by substitution.
`subs_max`	int	3	(since version 1.4.1) Maximum number of atoms to substitute in substitution
`ref_energies`	float [float …]		(since version 1.5.0) Reference energies for formation energy calculation [eV/atom]. Specify one value per atom type in the same order as `atype`, separated by spaces without parentheses or commas. The number of values must match the number of atom types in `atype`.
`end_point`	float [float …]		(deprecated since version 1.5.0) Kept for backward compatibility. Use `ref_energies` instead. Uses the same units and input format as `ref_energies`.
`emax_ea`	float	`None`	Energy upper limit (eV/atom) for computing the convex hull.
`emin_ea`	float	`None`	Energy lower limit (eV/atom) for computing the convex hull.

The following variables have been moved to the [visual] section since version 1.5.0.
cgen was deprecated in version 1.5.0.
The default values below apply to versions 1.4.3 and earlier. For version 1.5.0 and later, see the [visual] section.

Name	Value	Default	Description
`cgen`	int	`None`	(in versions 1.4.1–1.4.3) Which generation’s data to plot up to. If None, data will be plotted up to the latest generation.
`show_max`	float	0.2	When plotting the convex hull, the maximum value of the y-axis (for binary systems) or the maximum hull distance (for ternary systems) is set by show_max.
`label_stable`	bool	`True`	Whether to show stable compositions when plotting the convex hull.
`vmax`	float	0.2	Maximum value of the colorbar representing hull distance.
`bottom_margin`	float	0.02	Bottom margin of the y-axis for binary convex hull plot.
`fig_format`	str	`svg`	Figure format for convex hull plot: `svg`, `png`, or `pdf`.