A.K. Bakhshi

On the electronic structure and conduction properties of aperiodic DNA and proteins. I. Strategy and methods of investigations

Abstract The possibilites for applying the ab initio matrix block negative factor counting technique (NFC) for non-periodic nucleotide base stacks and for 4- and 5-component aperiodic model proteins are described. It is outlined how also correlation effects could be taken into account in an approximate way. After a brief summary of the basic equations of the NFC method the inverse iteration technique to study the Anderson localization of the wavefunctions belonging to the different energy levels is shortly reviewed. Also the calculation of hopping probabilities between different localization sites is sketched. Finally, the possibilites are outlined for the experiment verification of hopping conduction in proteins and (in a minor extent) in DNA, assuming the generation of free charge carriers in them through charge transfer.

On the electronic structure and conduction properties of aperiodic DNA and proteins. IV. Electronic structure of aperiodic proteins

Abstract Electronic density of states (DOS) curves of single stranded periodic and aperiodic DNA base stacks (in B conformation) and of a fragment of a human gene, obtained with the help of ab initio matrix block negative factor counting (NFC) method are presented. The calculated large values of band gap obtained for these systems rule out the possibility of intrinsic conduction in them. It is also found that in contrast to the corresponding period systems, the peaks in the DOS curves of aperiodic systems are broader. The probable effects of these changes in the DOS on the possibility of hopping conduction in DNA are also discussed.

On the observed high conductivity of poly(perinaphthalene) chains

Abstract Band-structure results of quasi-one-dimensional poly(perinaphthalene) (PPN) chains obtained on the basis of the ab initio Hartree-Fock crystal orbital method are presented. It is shown that due to the internal symmetry present in PPN, the band structure of PPN can be considered to be derived from the interaction of two cis -polyacetylene (PA) chains. The effects of geometry modification and of substitution at the carbon skeleton on the electronic properties of PPN are also discussed.

On the electronic structure and conduction properties of aperiodic DNA and proteins. III. The band structures of periodic polypeptides

Abstract In this paper the calculation of the energy band structure of periodic polypeptides using the ab initio Hartree-Fock crystal orbital method is described. Results are discussed for the twenty homopolypeptides in the β-pleated sheet configuration and for several periodic systems assuming the α-helix structure. The negative factor method in its matrix block form is used to provide density of states curve for periodic two-component polypeptides. The resulting properties of the band structure suggest that homopolypeptides and periodic more-component polyamino acids are in themselves insulators, but may become weak semiconductors if free charge carriers are generated in their valence or conduction bands, respectively, through charge transfer.

Effects of topology on the electronic properties of fused-ring polymers

Abstract Large differences in the band gap and other electronic properties between polyacene, polyphenanthrene and polybenzanthracene are rationalized by topological arguments. Ab initio crystal orbital calculations are reported for the three systems.

Electronic states of poly(thiophene-isothianaphthene) superlattices

Abstract The density-of-states curves of periodic and non-periodic poly(thiophene-isothianaphthene) block-copolymers of different composition have been calculated by the negative-factor-counting method. A discussion of the trends in band-gap variation is given.

The treatment of electron correlation in aperiodic systems. II. Applications to poly(Li2H2) and poly(acetylene, carbyne) chains

Abstract A new method for the calculation of the density of states of aperiodic polymers at the quasiparticle level (electronic structure with correlation) has been applied to poly (Li2H2) and to poly (acetylene, carbyne) chains. Both the periodic and the aperiodic copolymers have been studied.

On the electronic structure and conduction properties of aperiodic proteins: Study of six-component polypeptide chains

Abstract The results of the electronic density of states (DOS) of six-component periodic- and aperiodic peptide chains calculated on the basis of ab initio matrix block negative factor counting technique are presented. The six amino acid residues are glycine, serine, cysteine, asparagine, histidine and aspartic acid. In contrast to the periodic chains, aperiodic chains are found to have broader regions of allowed energy states. Large values of the fundamental band gap obtained for these systems rule out the possibility of intrinsic conduction in them. The study of the localization properties of the lowest unoccupied energy levels in the conduction band region of aperiodic chains on the basis of inverse iteration technique indicates these wavefunctions to be highly localized. In the light of these results, the possibility of charge transport through hopping conduction in proteins is discussed under the assumption of charge transfer from DNA to the polypeptide chains.

Theoretical design of polymers from topological arguments: electronic properties of polyisophenanthrene

Abstract Topological rules are discussed which describe the behaviour of the electronic properties of different fused-ring polymers. A new polymer, polyisophenanthrene (poly[3-4,4-3]phenanthrene), is suggested which should have a smaller gap than polyphenanthrene (poly[1-2,2-1]phenanthrene). Ab initio crystal orbital calculations are presented on polyisophenanthrene and related fused-ring polymers in order to check the topological predictions and to judge on topologically unrelated systems.

Effects of correlation and hydration on the electronic structure of aperiodic polypeptides

Abstract The effects of electron correlation and hydration on the density of the states of an aperiodic two-component polypeptide chain, containing glycine and alanine units, have been calculated using a combination of the Moller-Plesset many-particle perturbation theory and the negative-factor-counting method. It was found that correlation effects mainly shift the whole density of state curves, while hydration strongly influences the line shapes and widths.