The file

I J d BO. |

Here are

The angle terms follow, starting with the number of the angle terms. In each line is one angle term:

J I K wtyp θ nr_{JI} nr_{IK}. |

Here are

- wtyp = 1
- linear case
- wtyp = 2
- trigonal planar case
- wtyp = 3
- quadratic planar case
- wtyp = 6
- octahedral case
- wtyp = 9
- all other cases.

Then the torsion terms follow, starting with the number of the torsion terms. Each line contains one torsion term:

I J K L nr_{JK} ttyp φ θ_{IJK} θ_{JKL}. |

Here are

- ttyp = 1
*J*(sp^{3})-K (sp^{3})- ttyp = 11
- like ttyp=1, but one or both atoms are in Group 16
- ttyp = 2
*J*(sp^{2})-K (sp^{3}) or vice versa- ttyp = 21
- like ttyp=2, but one or both atoms are in Group 16
- ttyp = 22
- like ttyp=2, but
*J*or*K*is next a sp^{2}atom - ttyp = 3
*J*(sp^{2})-K (sp^{2})- ttyp = 9
- all other cases.

The inversion terms follow starting with the number of inversion terms
(e.g. the pyramidalisation of NH_{3}). In each line is one inversion
term:

I J K L ityp1 ityp2 ityp3 ω_{1} ω_{2} ω_{3}. |

- ityp = 10
- atom
*I*is C and atom*L*is O - ityp = 11
- like ityp=10, but
*L*is any atom - ityp = 2
*I*is P- ityp = 3
*I*is As- ityp = 4
*I*is Sb- ityp = 5
*I*is Bi- ityp = 9
- all other cases.

The nonbond terms follow starting with the number of the non-bonded terms. In each line is one nonbond term:

I J d . |

Here

If the determination of the molecule connectivity failed, you can specify the
block nxtnei12 in the
file `ufftopology`. Then the program calculates the other blocks.

Based on the numbers of the next neighbours (block nxtnei12 in the
file `ufftopology`) the program tries to determine
the UFF type of an atom. The following rules are implemented: If the
atom has three next neighbours and it is in the nitrogen group, then
it has a hybridization three. If it is not in the nitrogen group, it has
hybridization two. If the atom has four next neighbours and it is in
the carbon group, it has hybridization three. If it is not in the
carbon group, it becomes hybridization four. If the number of next
neighbours is six, then it gets the hybridization six.

Since the smallest eigenvalues *λ*_{i} of the Hessian has the
greatest influence on the convergence of the geometry optimization,
one can shift these values with

= λ_{i}⋅α + β⋅e^{-γx} |

and calculates a new Hessian with these modified eigenvalues.