Applications of the SCF-Xα Scattered-Wave Method to Molecular Crystals and Polymers

  • Keith H. Johnson
  • Frank Herman
  • Roland Kjellander
Part of the Nato Advanced Study Institutes Series book series (volume 9)


To facilitate the application of the self-consistent-field X scattered-wave (SCF-Xα-SW) method to certain types of molecular crystals and polymers, it is possible to introduce two modifications of the theory and computational procedure: (1) the use of overlapping atomic spheres and (2) the partitioning of the system into component interacting molecular units. The theoretical assumptions underlying the use of overlapping spheres are discussed first, and the theory is illustrated for molecular TCNQ, a component of highly conducting organic molecular crystals of the TTF-TCNQ type. The results obtained for TCNQ suggest that the SCF-Xα-SW method, in conjunction with overlapping atomic spheres, can be used to produce realistic electronic energy levels and charge distributions for large planar organic molecules. To calculate the electronic structure of a crystalline or polymeric array of interacting polyatomic molecules, it is possible to make use of some unique features of the SCF-Xα-SW method. The calculations are carried out on one part of the system at a time using overlapping atomic spheres and a local intersphere potential, iterating between interacting parts until self consistency is attained. By exploiting the local molecular symmetry of each component part, the calculations can be further simplified, and only moderate amounts of computer time are required. This method is not dependent on the assumption of molecular periodicity or Bloch’s theorem and therefore is applicable to disordered or amorphous polymers and molecular solids, where there is at most only short-range molecular order. Results for a water trimer are presented as a simple illustration of the computational procedure for a weakly coupled polymer. Extensions of this procedure to more complex systems, such as the molecular crystal TTF-TCNQ, are also discussed.


Molecular Crystal Outer Sphere Secular Equation Atomic Sphere Energy Level Structure 
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Copyright information

© Plenum Press, New York 1975

Authors and Affiliations

  • Keith H. Johnson
    • 1
  • Frank Herman
    • 2
  • Roland Kjellander
    • 3
    • 4
  1. 1.Department of Metallurgy and Materials ScienceMassachusetts Institute of TechnologyCambridgeUSA
  2. 2.IBM Research LaboratorySan JoseUSA
  3. 3.Department of Physical ChemistryThe Royal Institute of TechnologyStockholm 70Sweden
  4. 4.Department of Metallurgy and Materials ScienceM.I.T.USA

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