The noen energy is the sum of N_noe terms where each term has the form:

khi ( rij - rhi )n, if rij < rhi
   0, if rlo <= rij <= rhi
   klo ( rlo - rij )n, if rij < rlo

where n is an integer greater than 1, k_hi and k_lo are force constants, r_ij the current distance between atoms atom_i and atom_j and r_hi and r_lo are the edges of the potential well. This function allows a flat-bottomed potential well to be constructed (among other things). Normally, k_hi and k_lo are equal quantities but one can specify different values for these constants to construct a potential well that has different slopes at the two ends. The noen record in the descriptor file has the form

noen	Nnoe
	atomi	atomj	n	klo	rlo	khi	rhi
	...	...	...	...	...	...	...

The noen record starts with the keyword noen followed by the number of terms N_noe., then N_noe lines of seven fields each: the pair of interacting atoms atom_i and atom_j, the power n, the force constant on the lower edge of the potential well k_lo, the position of the lower edge r_lo, the force constant on the upper edge of the potential well k_hi and the position of the lower edge r_hi. There must be exactly N_noe such records. Example:

noen   5

1   101   2   0   0   21184.1   100
2   101   2   0   0   21184.1   100
3   101   2   0   0   21184.1   100
4   101   2   0   0   21184.1   100
5   101   2   0   0   21184.1   100

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A noen record containing five terms. Each term constrain one of five atoms (1 to 5) to a sixth atom (101) with a flat-bottomed potential where the potential has no effect for distances from 0 to 100 angstroms. Beyond this distance the five atoms will feel the effects of a harmonic function that pulls the atoms towards atom 101. Thus, the five atoms 1 to 5 are constrained to inhabit a sphere of radius 100 angstrom centered on atom 101. When the atoms are inside the sphere this energy term does not contribute anything to the energy of the atoms.