GEOMETRY OPTIMIZATION OF POLYMERS BY THE ELONGATION METHOD

Theoretical studies on the electronic and the geometrical structures f or various molecules by the molecular orbital or the density functiona l theory have recently been developed and applied widely under the pro gress of computer technologies. At present, it is possible to carry ou t a theoretical investigation on electronic properties for small molec ules at the Hartree-Fock and the post-Hartree-Fock levels by the impro vement of advanced program packages. However, it is difficult to perfo rm the theoretical calculations on electronic structures for large pol ymers with the aperiodic sequence of molecular segments, because the t heoretical treatment of random systems has not yet been established. W e recently proposed the elongation method as a useful theoretical appr oach to obtain the electronic states of any polymers without the perio dic geometry of molecular fragments. in the previous works, the reliab ility of our treatment has been shown by the application to many polym ers under single-point calculations with fixed molecular geometry. Thu s, as the next step of our study, an attempt for the geometry optimiza tion of large polymers by the elongation method was made in this work. As the first samples of geometry optimization, the periodic polymers of polyethylene, polyacetylene, and polyglycine were examined. Also, a s the second samples, the locally aperiodic polymers of polyacetylene with local defects of positively and negatively charged solitons were tested. Total energies, optimized geometries, and electron densities w ere checked by those obtained from the conventional molecular orbital method. (C) 1997 John Wiley & Sons, Inc.