The stud energy is the sum of N_stud terms where each term has the form:

ks { ( xi - xo )2 + ( yi - yo )2 + ( zi - zo )2 }

where k_s is a force constant, x_i, y_i and z_i are the current cartesian coordinates of atom_i and x_o, y_o and z_o are the cartesian coordinates to which atom_i is to be fixed. Note that the atom will orbit the desired position and the deviation from ideality (where atom_i is exactly at x_o, y_o,z_o) depends on the value of k_s. The stud record in the descriptor file has the form

stud	Nstud
	atomi	ks	xc	yc	zc
	...	...	...	...	...

The stud record starts with the keyword stud followed by the number of studded atoms N_stud, then N_stud lines of five fields each: the atom number of the atom to be studded atom_i, the force constant k_s and the desired position of the atom x_o, y_o and z_o. There must be N_stud such records. Example

stud   1

101   10032.61   0.0   0.0   0.0

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A stud record containing one atom to be studded. This is atom 101 which is to be studded to the origin (0,0,0). A light constraint is used with a force constant of 10032.61 CEU Å^-2 (24 kcal/mol/Ų).