Nonbonding intermolecular forces: The tetrathiafulvalene (TTF) dimer

It is shown that the simplified version of local density functional theory proposed by Gordon and Kim can be used to accurately determine the location of interaction energy minima associated with large π orbital planar molecules interacting at van der Waals distances. The results of this calculation have contributed to the understanding of the origin of tetrathiafulvalene (TTF) stacking in neutral crystalline TTF and in the quasi-one-dimensional organic conductor, tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). This technique should be generally useful in determining the origin of the stacking geometries of large planar molecules such as, for example, observed between nucleic acid constituents. © 1980 American Institute of Physics.