  This paper presents a proposal of a rather new type of effective interatomic
interaction for molecular dynamics and similar applications. The model consists
of atoms with prescribed geometric arrangement of active orbitals, represented
by arms of the length of half of the relevant bond lengths. The interactions
have a repulsive part between the atomic centers and an attraction between the
arm ends of different atoms. For each atom pair only the closest pair of arms
interacts attempting to form the bond. This is a picture of sigma bonds, the pi
bonds are modeled by alignment of additional internal vectors which might
characterize a given atom. Also these are primarily pair interactions. Thus
there are only pair interactions of several types present. The intrinsic
arrangement of the model elements, arms and internal vectors can be switched
depending on the environment. Thus the complexity of the many-body potentials
is replaced by pair interactions between atoms with complex internal behaviour.
The proposed model thus allows formation of new geometries, establishing new
and breaking existing bonds with the use of only pair interactions and
environment scanning. We discuss in some detail the carbon case and shortly
also hydrogen, silicon and sulfur.
