# fukui

Compute atom-resolved Fukui reactivity indices.

The algorithm computes derivatives of charge populations with respect to electron number, using either analytic or numerical differentiation. See for example Yang and Mortier, JACS, 108, 5708 (1986) for the definition of the key quantities.

The input should contain structure and and one suitable method subcommand. Options specifying the underlying population analysis can be specified through the population subcommand.

For example, Fukui indices can be computed as follows:

fukui(
structure(molecule = methanol)
population(method = mulliken)
xtb()
)


For the frontier-molecular-orbital method, a previous SCF calculation can be loaded, as in

ch3oh := xtb(
structure(molecule = methanol)
)
fukui(
method = fmo
)


This command can appear in the global context.

### Options

charge_delta

Amount by which to change total molecular charge in the finite difference calculation.

• The type is real
• The default is 0.01
• The value must be positive
degeneracy_threshold

Energy threshold for determining whether orbitals are degenerate. This option applies for algorithms that require specific identification of HOMO and LUMO orbitals.

• The type is real
• The default is 1e-3
• The value must be nonnegative
load

Name of a result set from an SCF calculation to load for computation of the Fukui indices.

• The type is string
• There is no default value.
method

Determine the method used to compute the Fukui indices.

• The type is string
• The default is numerical
• The value must be one of:
• fmo - Use the charges of the HOMO and LUMO (frontier molecular orbitals) to determine the Fukui indices. This corresponds to analytic differentiation with respect to electron number in the fixed-orbital approximation.
• numerical - Use a finite-difference derivative to determine the Fukui indices.
name

Specify the name of a set of results.

This option is deprecated.

• The type is string
• There is no default value.
print_level

Print level.

• The type is int
• There is no default value.
• The value must be one of:
• -2 - No output
• -1 - Minimum output
• 0 - Output that doesn't scale with system size
• 1 - Output that scales linearly with system size
• 2 - (Debugging) output that scales quadratically with system size
• 3 - (Debugging) output that scales cubically with system size