# coordination_number

Define a coordination number between a reference atom j and coordinated atoms i. The length scale c is proportional to the cutoff distance for coordination. Parameters n (numerator_exponent) and m (denominator_exponent) control the rate of decay in coordination number (e.g., larger n leads to a sharper dropoff from 1 to 0). \begin{align} CN = & \sum_i \frac{1 - (\frac{r_{ij}}{c})^n}{1 - (\frac{r_{ij}}{c})^m} \end{align}

aimd(
structure(molecule = water)
xtb(model = gfn0)
n_steps = 40
harmonic_spring(
force_constant = 0.0001 au
coordination_number(
reference_atom = 1
coordinated_atoms = [2, 3]
length_scale = 2.0 bohr
numerator_exponent = 12
denominator_exponent = 6
)
)
)

This command can appear in the global context.

### Options

coordinated_atoms

Indices of coordinated atoms. Index starts at 1.

This option is mandatory.

• The type is [int]
• There is no default value.
• The value must be positive
denominator_exponent

Value of m, in the denominator. The exponent m is usually less than n.

This option is mandatory.

• The type is int
• The default is 6
• The value must be nonnegative
length_scale

c parameter

This option is mandatory.

• The type is quantity
• There is no default value.
numerator_exponent

Value of n, in the numerator. Smaller n indicates a smoother coordination number.

This option is mandatory.

• The type is int
• The default is 12
• The value must be nonnegative
reference_atom

Index of reference atom. Index starts at 1.

This option is mandatory.

• The type is int
• There is no default value.
• The value must be positive
value

Reference coordination number value specified. If not supplied, the coordination number of the input structure is used.

• The type is real
• There is no default value.
• The value must be nonnegative