We present here a novel approach to the determination of the interaction between two atoms, each in a P-2 electronic state, embedded in a cluster of spherical atoms. The model requires accurate ab initio potential energy curves for the M-2 system, for all the 36 electronic states which correlate with dissociation into ground-state M(P-2) atoms. Consequently, making use of a valence-bond-like model, we transform these 36 molecular orbital states into a set of 36 Cartesian (q(a)q(b)) states which correspond to assigning the two p electrons to Cartesian orbitals centered on either atom. It is then easy to use the earlier Balling and Wright model [L. C. Balling and J. J. Wright, J. Chem. Phys. 79, 2941 (1983)] to determine, in this 36 state basis, the matrix elements corresponding to the interaction of each P-2 atom with any number of surrounding spherical ligands. The lowest eigenvalue of the resulting 36x36 matrix defines, in an adiabatic approximation, the potential governing the motion of the atoms. We apply this approach to the determination of the interaction of two Al atoms embedded in solid pH(2), site-substituted in the center of two adjacent hexagons. We find the interaction between the two Al atoms to be significantly modified by the presence of the intervening pH(2) molecules.