Specify a link atom for terminating the high-level subsystem in an ONIOM calculation. This command can appear in the global context.

### Options

connecting_atom

Specify the index of the atom to which the link atom is bonded. If the value is not specified, the program will automatically determine the index based on the value of replaced_atom, and the connectivity of the system.

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

Specify the index of the atom to be replaced by the link atom. If input value is not specified, the program will automatically determine the index based on the value of connecting_atom, and the connectivity of the system.

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

Specify the scaling factor which is defined as the ratio between the bond length of (link atom-connecting atom) and the bond length of (replaced atom-connecting atom). If input value is not specified, the program will automatically determine the value based on the covalent radii of LA, CA and RA, according to this paper. An exmaple input: link_atom( symbol = 'H' connecting_atom = 2 replaced_atom = 3 scale_factor = 0.7 ) will add a link atom hydrogen between the second and third atoms in the molecule with a scaling factor of 0.7.

• The type is real
• There is no default value.
symbol

Specify the atomic symbol of the link atom;

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