The mors morse bond energy is the sum of N_morse terms where each term has the form:

Eo { 1 - exp[ -a( bij - bo ) ] }2
   

where E_o is a base energy [CEU], a a stretch constant [Å^-1], b_ij the current bond length between the atoms atom_i and atom_j and b_o the equilibrium or ideal bond length [Å]. Very roughly, E_o determines the height of the energy barrier to bond breakage, and a controls the width of the energy well.

The mors record in the descriptor has the form:

mors	Nmorse
	atomi	atomj	Eo	a	bo
	...	...	...	...	...

The mors record starts with the keyword mors followed by the number of morse bonds N_morse, then N_morse lines of five fields each: the pair of atoms that make up the bond atom_i and atom_j, the base energy E_o, the constant a and the equilibrium bond length b_o. Example:

mors 1

3   56   10453   1.5   1.54

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A single morse bond between atoms 3 and 56 with a base energy of 10453 CEU (25 kcal/mol) and an equilibrium bond length of 1.54Å.