Sambhu N. Datta

DIRAC-HARTREE-FOCK THEORY AND COMPUTATIONAL-PROCEDURE FOR MOLECULES

Abstract A general approach has been developed which allows relativistic Dirac-Hartree-Fock calculations for molecules. Integrals are formed by expanding basis atomic spinors in gaussian functions. Calculations are reported for Be and Be 2 . It is shown that negative-energy corrections have only a slight effect in molecular calculations of this type.

Analysis and merit of the constrained-component variation in dirac theory

It is shown that the constrained-component variation generally suggested by Rosicky and Mark is very fundamental, has consistent variational features and reproduces, as a special case, earlier variational results for atomic systems obtained by Drake and Goldman. Numerical merits and demerits of this method are qualitatively assessed.

Semiempirical quantum chemical calculation on the chlorophyll—water system and determination of excitonic characteristics of a model chloroplast

Abstract Molecular orbitals of the chlorophyll—water system and its dimer have been calculated by the CNDO method. The CNDO/S excitation energies have been computed. Excitonic characteristics of a model crystal of chlorophyll—water molecules have been calculated. The dimensions of the model crystal are same as those of a typical thylakoid unit. Characteristics of the trap (chlorophyll special pair) have also been determined.

Relativistic extension of the Hohenberg-Kohn theorem

Using the configuration-space HamiltonianH+ which is derivable within the framework of quantum electrodynamics, we extend the Hohenberg-Kohn theorem to the relativistic theory of electrons in atoms or molecules.

Molecular orbital calculations on Fe4(CO)10(μ-CO)(μ-Se)2 and Fe3Ru(CO)10(μ-CO)(μ4-Se)2

Molecular orbital calculations using the extended Huckel program were carried out on Fe4(CO)10(μ-CO)(μ4-Se)2 and Fe3Ru(CO)10(μ-CO)(μ4-Se)2. On the basis of a molecular orbital description, binding energy, polarity and the metal-metal bond order were found to decrease on substitution of one Fe atom of Fe4(CO)10(μ-CO)(μ4-Se)2 by a Ru atom.

Relativistic quantum chemistry and rigorous variational analysis

A brief review of relativistic quantum chemistry is given here. Relativistic effects and their importance in chemistry are discussed. An outline of different theoretical aspects is presented. Aspects of variation techniques relevant to relativistic calculations are discussed in detail. These involve the derivation of min-max theorems for Dirac, Dirac-Hartree-Fock and Dirac-Coulomb calculations. The consequence of relativistic Hamiltonians being unbounded are also discussed for other lines of investigation. The upper bounds derived are physically interpreted. Sample Dirac-Hartree-Fock results for the Be atom, calculated using both STO and GTO bases for the nonrelativistic orbitals and the upper components of the relativistic orbitals, are given. The inadequacy of the so-called kinetically balanced basis set is discussed and illustrated with these results. The importance of the variational or dynamical balance and hence the merit of the LCAS-MS scheme is pointed out. The possibility of calculating quantum electrodynamical pair energy from relativistic configuration interaction calculations on a two-electron atom is discussed and exemplified. The present status of relativistic molecular calculations is briefly reviewed. Conclusions on the aspects of variational analysis and molecular calculations are enclosed.

Ab-initio nonrelativistic and relativistic Hartree-Fock calculations for both closed- and open-shell molecules using GTO basis

Computer programs forab-initio Hartree-Fock and Dirac-Hartree-Fock calculations on closed- and open-shell atoms and molecules have been indigenously developed. Sample results of high quality are given for Li, Be, LiH and Be2. As a byproduct of these calculations the importance of considering relativistic effects in the investigation of the elusive bound-state structure of Be2 is clearly indicated.

Semi-empirical Hartree—Fock calculations on the mechanism of enniatin B mediated transport of sodium ions

Abstract The passage of sodium ions through enniatin B is studied by the CNDO method. Electronic dissociation energy of the enniatin Bue5f8Na+ complex in water is 0.496 au for the open form (0.397 au for the closed form). The open complex is found to be more stable than the closed one in water. The dissociation energy changes when counterions representing charged heads of phospho-lipids are placed around the ionophore. Variation of counterion charges leads to different possibilities for the transport of Na+ across a lipid membrane. These are (i) no transport, (ii) transport through channels and (iii) transport of the ion—ionophore complex. A pH dependence that relies on the nature of counterion charges is predicted for the transport.

Quenching of excitations in an impure molecular crystal

The rate of quenching of excitons in a one-dimensional molecular crystal by an impurity is quantum-mechanically calculated.

Fluid-dynamical representations of the Dirac equation

A relative kinetic mass operator is defined bym =c−2·(E −eΦ), and it is shown that bt using it in a symmetric form one can correlate the (charge) velocity operatorα in the Dirac theory exactly with the general quantum mechanical momentum —ih∇. Then the net force, defined as the rate of change of the relative momentum with time, is exactly equal to the Lorentz force. The contribution due to the time variation of mass equals the negative of space variation of the scalar potential, the Newtonian force, whereas the time variation of the charge current absorbs the entire vector potential dependence. The analogous Euler equations can be written either in terms of the charge current or in terms of the mass current. For a many particle system one needs the usual net single particle parameters and the consideration of both the direct and exchange contributions of the two particle interaction. These Euler equations yield two different conditions of the stationary state. It is shown that the charge-current condition is necessary but not sufficient, whereas the mass-current condition retains the appropriate scalar potential dependence. These two conditions are compared for the spherically symmetric case. The charge density, charge current and relative mass current are tabulated for atomic spinors. Differences between the quantum and classical forces for the H2+ molecular ion exhibit the inadequacy of ordinary atomic spinor basis in forming molecular spinors.