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The present numerical, time-dependent density-functional study of a He atom interacting with strong, oscillating magnetic fields shows that this scenario is quite different from the case of a laser electric field-He atom interaction. Signatures of sluggish electron dynamics are found in this study, while through a mechanical analogy the flow of electron density under such conditions has been explained. These calculations take into account both exchange and correlation. Through several calculated dynamical quantities, we have shown that, in contrast to the case of the (one-electron) H atom studied earlier, the nonlinear dependence of interelectronic repulsions (a combination of Coulomb, exchange and correlation terms) on the magnetic field plays a significant role in this strong-field electron dynamics in the He atom, which cannot be explained by a perturbative approach. [ABSTRACT FROM AUTHOR]

This work reports the study of silver ion dynamics in Ag2S-doped silver molybdate–glass nanocomposites of compositions xAg2S–(1 – x)(yAg2O–(1 – y)MoO3). The volume fraction of crystalline phases in these glass nanocomposites increases with the increase of Ag2S content and considerably influences the dc conductivity. It is observed that a significant amount of volume fraction of crystalline phases for x≥ 0.15 for the y= 0.20 series and for x= 0.20 for the y= 0.30 series causes the conductivity to decrease. The power law exponent has been obtained from ac conductivity spectra using the power law model and is observed to be almost constant at lower volume fraction of the nanocrystalline phases embedded in the glass matrix, but it decreases for samples with high crystalline volume fraction. The electric modulus data have been analyzed on the basis of the Havriliak–Negami (HN) equation. The Kohlrausch–Williams–Watts (KWW) stretched exponent β, obtained from modulus data, indicates a strong nonexponential relaxation. The scaling of the conductivity spectra reveals that the relaxation dynamics is independent of temperature but is dependent on compositions affected by the increased volume fraction of crystalline phases of the glass nanocomposites.

Abstract: For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schrödinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities,I = 1 × 108, 1 × 1013, 5 × 1016, and 5 × 1018 W cm−2 respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed.

Boron nitride films were synthesized by r.f. plasma CVD technique using borane-ammonia, nitrogen and argon as the precursor gases. The films were deposited onto Si (100) and fused silica substrates kept at different substrate temperatures (573–703 K). Hot emissive probe was utilized to measure the ion energy of the radicals bombarding the substrate during deposition. Effects of substrate temperature, ion energy and ion current on the c-BN content in the films were determined. Bombardment of energetic ions during growth has profound effect on the film quality. Initial layer seemed to contain boron rich hexagonal B51–2 N phase.

Time-dependent Schrödinger equation (TDSE) is solved numerically to calculate the ground- and first three excited-state energies, expectation values 〈x2j〉, j=1, 2 …, 6, and probability densities of quantum mechanical multiple-well oscillators. An imaginary-time evolution technique, coupled with the minimization of energy expectation value to reach a global minimum, subject to orthogonality constraint (for excited states) has been employed. Pseudodegeneracy in symmetric, deep multiple-well potentials, probability densities and the effect of an asymmetry parameter on pseudodegeneracy are discussed.

Based on the system-reservoir description, we propose a simple solvable microscopic model for a nonequilibrium bath. This captures the essential features of a nonstationary quantum Markov process. We establish an appropriate generalization of the fluctuation-dissipation relation pertaining to this process and explore the essential modifications of the Bloch equations to reveal the nonexponential decay of the Bloch vector components and transient spectral broadening in resonance fluorescence. We discuss a simple experimental scheme to verify the theoretical results.

Earlier work on internal stresses in one-electron systems is now extended to many-electron systems. The expressions for local stresses and local force densities involve electrostatic fields arising from given electronic and nuclear charge distributions and, therefore, the stress at any point in 3-D space again assumes a maxwellian form. As an illustration of the stress formalism, the interaction between two many-electron systems has been considered, taking the formation of the hydrogen molecule from its constituent atoms as a simple example. Using the double-zeta gaussian wavefunctions of Snyder and Basch, the stresses and fields experienced by an observer at three points on the internuclear axis are evaluated as functions of the internuclear distance R, and their respective variations are rationalized by means of classical arguments. The most interesting observation is that, depending on the location of the point considered, the interaction stress or the total stress or both may either vanish or pass through an extremum at an R value close to Req. The consequences of a charge build-up in the binding region are clearly apparent. The picture of chemical binding in the H2 molecule that emerges from these calculations is a local one in which binding occurs due to variations of electrostatic pressure from point to point in such a manner as to cause the vanishing of either the total electrostatic force density or the difference force density or both at certain points on the internuclear axis; this complements the existing viewpoints on binding in the molecule. It may not be too early to say that the stress formalism which includes the Hellmann-Feynman force viewpoint as a special case has the potential to develop into a powerful interpretive tool for understanding molecular phenomena.

In this paper a generalized concept of stresses in molecular systems is presented. The stress tensor in the 3-D space of a molecule, defined in terms of internal fields arising from its nuclear and electronic distributions, has components with forms reminiscent of Maxwell's stress tensor for classical electromagnetic fields. As an illustrative example, the stress tensor has been calculated for the 1s, 2s and 2px states of the hydrogen atom. The physical significance of the various components of the stress tensor is also examined. The stress concept is likely to yield considerable insight into molecular phenomena such as chemical binding, molecular geometry, chemical reactivity and transferability of fragment properties from one molecule to another.

Using the double-zeta wavefunctions of Snyder and Basch [5], the Weizsäcker correction $$T_w = \tfrac{1}{8}\int d \vec r(\nabla \rho \cdot \nabla \rho )\rho ^{ - 1} $$ has been evaluated for the molecules H2, HF, BF, N2 and CO. There was no linear correlation between Tw and the binding energy for these molecules.

Using a very simple trial function and unperturbed electron densities calculated by a new procedure, the frequency-dependent dipole polarizability a (?) of Ne, Ar, Kr and Xe has been calculated in the range 0 = ? = 0.45 a.u., by a Karplus-Kolker-type variation-perturbation method. Results progressively worsen for larger systems so that, for Xe, a(0) is only 75% of the experimental value. Probable reasons for this are discussed.

Abstract: There are three reasons for seeking an alternative density-based quantum mechanics of many-electron systems, incorporating both interpretive and basic quantum mechanical aspects: (i) failure of popularad hoc chemical concepts underab initio scrutiny; (ii) failure ofab initio calculations to provide simple concepts; and (iii) highly attractive concepts and pictures generated by the electron density in three-dimensional space. At present the three interlinked pillars for such a density mechanics (in contrast to wave mechanics) are: (a) density functional theory; (b) quantum fluid dynamics; and (c) property densities in three-dimensional space. This article describes several studies dealing with these aspects. Although a density mechanics may well be an impossible ideal to realize, the search for it is indeed rejuvenating the whole of quantum chemistry.

Studies on gas-surface dynamics have acquired considerable importance recently not only for their intrinsic scientific interest but also for their technological potential. This article first briefly describes various experimental techniques and a number of interesting recent observations resulting from these techniques. It then discusses certain important theoretical methodologies being extensively used nowadays. There arethreebroad overlapping streams of theoretical works, viz classical, semi-classical and quantum-mechanical. There are alsothreebasic problems in gas-surface interaction, viz (i) the interface presents a manybody problem; (ii) the solid surface is “rough”; (iii) the number of diffractive and inelastic channels is enormously large. The semi-classical approaches appear to dominate over the others in variety and quantity. But the sources of benchmark theoretical results are still the rigorous classical-trajectory and close-coupling quantum-mechanical calculations. The coming years are likely to witness not only increased numerical accuracy through refinements in semi-classical and quantum-mechanical approaches, but also certain special approximate methods designed to yield deeper physical insights into the nature of gas-surface interaction.

Abstract: Accidental degeneracy seems to be the rule rather than an exception amongst thed orbital energies of substituted octahedral complexes ofd 1 configuration. By using symmetry and physical arguments, in conjunction with first-order and second-order degenerate perturbation theory, it is shown that such accidental degeneracies arise in crystal-field theory due to the choice of an inflexible basis set of metal orbitals which neglects the polarisation of metal orbitals by the ligand charges.

Triply excited states of many-electron atomic systems are characterized by the presence of strong electron correlation, closeness to more than one threshold, and degeneracy with many continua; therefore, they offer unusual challenges to theoretical methodologies. In the present article, we computed with reasonable accuracy all the n=2 intrashell triply excited states (2s²2p ²P; 2s2p^2 2D, ⁴P, ²P, ²S; and 2p^3 2D, ²P, ⁴S) of three-electron atomic systems (Z=2, 3, 4, 6, 8, 10) by using a density functional formalism developed recently in our laboratory, based on the nonvariational Harbola–Sahni exchange potential in conjunction with a parametrized local Wigner and Lee–Yang–Parr correlation potentials. Nonrelativistic energies and densities are obtained by solving a Kohn–Sham-type differential equation. The calculated results are compared with available experimental and other theoretical data. The 2p³(⁴S)→1s2p²(⁴P) transition wavelength for the isoelectronic series is also computed. The overall good agreement of our results with the literature data indicates the reliability of the present density functional methodology for excited states of many-electron systems. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 317–332, 1997

A new local density functional approach for the calculation of correlation energies of many-electron atomic systems is proposed by using the exact results for the correlation energy of a two-electron system bound by a harmonic oscillator external potential. This is motivated by the fact that the correlation energy is a universal functional of the electron density, and the form of this functional is independent of the external potential. The calculated numerical results for the correlation energies show very good agreement with the standard values reported in the literature. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 461–465, 1997

Self-consistent density-functional calculations, in an exchange-only framework, are reported for the energies and moments of the 23S excited states of the helium isoelectronic sequence, according to the prescription of Harbola and Sahni. The total energy values show excellent agreement with “exact” nonrelativistic values while the moments are also quite satisfactory.

The lattice gas automata (LGA) technique as an alternative to the partial differential equation (PDE) approach for studying dynamical processes, including those in reaction-diffusion systems, is reviewed. The LGA approach gained significance after the simulation of Navier-Stokes equation by Hardyet al(1976). In this approach, the dynamics of a system are simulated by constructing a microlattice on each node of which Boolean bits are associated with the presence or absence of particles indistinctvelocity states. A complete description involves the composition of anelastic collision operator, areactive collision operatorand apropagation operator.The Hardy, de Pazzis and Pomeau (HPP) model does not have the desired isotropy, but its subsequent modification in 1986, known as the Frisch, Hasselacher and Pomeau (FHP) model (Frischet al1986), has been applied to a variety of nonequilibrium processes. Reaction-diffusion systems have been simulated in a manner analogous to the master equation approach in a continuum framework. The Boltzmann kinetic equation as well as the expected complex features at the macroscopic level are obtained in LGA simulations. An increasing trend is to use real numbers instead of Boolean bits for the velocity states. This gives the lattice Boltzmann (LB) model which is not only less noisy than LGA but also numerically superior to finite-difference approximations (FDAs) to PDEs. The most significant applications of LGA appear to be in the molecular-level understanding of reactive processes.

There are three reasons for seeking an alternative density-based quantum mechanics of many-electron systems, incorporating both interpretive and basic quantum mechanical aspects: (i) failure of popularad hocchemical concepts underab initioscrutiny; (ii) failure ofab initiocalculations to provide simple concepts; and (iii) highly attractive concepts and pictures generated by the electron density in three-dimensional space. At present the three interlinked pillars for such a density mechanics (in contrast to wave mechanics) are: (a) density functional theory; (b) quantum fluid dynamics; and (c) property densities in three-dimensional space. This article describes several studies dealing with these aspects. Although a density mechanics may well be an impossible ideal to realize, the search for it is indeed rejuvenating the whole of quantum chemistry.

The method of local scaling transformation in density functional theory calculates a transformation function (TRF) in order to generate an optimized atomic N-electron wave function from a trial density and a reference density/wave function. The TRFsf(r) for several atomic systems are studied and it is observed that the number of minima in df(r)/drequals the number of atomic shells, except whenρ=ρ0andf=r.

A comprehensive, nonperturbative, time-dependent quantum mechanical (TDQM) approach is proposed for studying the dynamics of a helium atom under an intense, ultrashort (femtoseconds) laser pulse. The method combines quantum fluid dynamics (QFD) and density functional theory. It solves a single generalized nonlinear Schrödinger equation of motion (EOM), involving time and three space variables, which is obtained from two QFD equations, namely, a continuity equation and an Euler-type equation. A highly accurate finite difference scheme along with a stability analysis is presented for numerically solving the EOM. Starting from the ground-state Hartree–Fock density for He at t=0, the EOM yields the time-dependent (TD) electron density, effective potential surface, difference density, difference effective potential, ground-state probability, 〈r〉, magnetic susceptibility, polarizability, flux, etc. By a Fourier transformation of the TD dipole moment along the linearly polarized-field direction, the power and rate spectra for photoemission are calculated. Eleven mechanistic routes for photoemission are identified, which include high harmonic generation as well as many other spectral transitions involving ionized, singly excited, doubly excited (autoionizing), and continuum He states, based on the evolution of the system up to a particular time. Intimate connections between photoionization and photoemission are clearly observed through computer visualizations. Apart from being consistent with current experimental and theoretical results, the present results offer certain predictions on spectral transitions which are open to experimental verification. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 441–474, 1998

The INDO-MO calculations on [6]-helicene reported here enable one to classify the four HOMO's as predominantly π, in contrast to other occupied MO's. A linear adjustment of these four HOMO's correlates well with the experimental photoelectron and optical spectra. Viewed through Mulliken's overlap population between overlapping rings, the transannular interaction in [6]-helicene appears to be unfavourable and therefore minimised. The use of a skeleton representation of the molecule is considered and found inadvisable.

Our objective was to assess HIV risk perceptions, risk behaviours and factors that may facilitate an increase in injection drug use in Calcutta. Focus group discussions and in‐depth interviews were conducted with a selected group of drug users to delineate drug use patterns, languages used to express addictive and related experiences and acceptance of harm minimization messages. Results from these were used to develop a semi‐structured interview instrument which was used to interview 111 drug users (76 IDUs and 35 non‐IDUs) recruited from jails and detoxification centres. Secondary data of narcotic seizures for the last 5 years were collected from the Calcutta police department. Data on percentage of IDUs admitted to large detox facility in the city was also collected. Findings show that HIV/AIDS knowledge and risk perceptions were low; sharing of injection equipment was reported by 66% of the injectors; and condom use was insignificant. Non‐availability, rising cost and increasing tolerance to heroin were cited as factors contributing to switch to injection. Ecological association was found between intensified police activity and an increase in: the amount of smokable heroin seized; increased injection of buprenorphine; and admission to detoxification centres. In addition to HIV, IDUs were also found to be prone to hepatitis B and C. The findings suggest an urgent need for developing and implementing community‐based HIV prevention interventions targeting drug users in Calcutta.

Density functional theory (DFT) has not been applied on a large scale to time-dependent problems and problems involving excited states. Atomic and molecular collisions involving both these types of phenomena remain outside the purview of DFT. An amalgamation of quantum fluid dynamics (QFD) with DFT considerably broadens the range of applicability of traditional (ground-state) DFT. Ion-atom collisions have been studied by jointly using DFT and QFD.

A quantum hydrodynamical study is made of the dynamical changes of a helium atom interacting with lasers of two different intensities, but having the same frequency. Under the intense laser field, electron density oozes out of the helium atom by absorbing laser photons and getting promoted to higher excited states including the continuum. Under the superintense field, electron density partly moves away from the helium nucleus but remains in the “quasi-bound” dressed states along with the laser field, thus suppressing ionization.

The electron density distribution in a molecule determines its stability, geometry and reactivity, in short its chemistry.

Threesimulatedexpressions are suggested regarding the Z-dependence of groundstate energies of neutral atoms at the Hartree-Fock, exact nonrelativistic and relativistic levels. The Hartree-Fock-level Z−1/3-expansion contains three previously derivedplustwo newly derived terms, the latter signifying exchange corrections from the ‘inner core’ and the ‘core mantle’ of the Lieb atom. This leads to better agreement than any previous expression, with every coefficient being physically transparent. The Z-dependence of the correlation energy is obtained from a semiempirical Wigner-type correlation potential while the relativistic correction is taken to be in between the values suggested separately by Scott and Schwinger. Agreement with reference values is again better than before. It appears, however, that the atomic Z−1/3-expansion should not proceed beyond terms O(Z).

Abstract: According to the open-shell CNDO/2 calculations on ClF2, performed by using the computer programme developed by Pople, Beveridge and Dobosh, the molecule is linear and stable, with equilibrium bond length 1.507Å and binding energy −173.7 kcal/mole. The molecule has a tendency to dimerise and to disproportionate into ClF3 and ClF. The netd-orbital population in the monomer is 0.88. Bonding characteristics and other molecular properties are also discussed.

Abstract: For a closed-shell molecule, a connection is drawn between two recent models for molecular shapes, namely, those based on the second-order Jahn-Teller (SOJT) effect and the highest occupied molecular orbital (HOMO) postulate respectively. Two necessary and sufficient conditions are derived within the molecular orbital framework for the approximation inherent in the SOJT model to be valid. One of these conditions is akin to the HOMO postulate.

A nonperturbative, time-dependent (TD) quantum mechanical approach is described for studying the collision dynamics between the He atom and a fully stripped ion. The method combines quantum fluid dynamics and density functional theory to solve two coupled equations: one for the trajectory of the projectile nucleus and the other for the electronic charge distribution of the target atom. The computed TD and frequency-dependent properties provide detailed features of the collision process. Inelastic and ionization cross sections are also reported. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 251–271, 1998

A simple treatment of the static Jahn-Teller effect in the ground state of VCl4 is made along the lines of the force formulation of Clinton and Rice. Assuming that the doubly-degenerate e-type orbital responsible for the deformation is simply a 3d atomic orbital on the vanadium atom, it has been shown, using Watson's SCF atomic orbitals, that the static distortion from an idealized tetrahedral shape is so small as not to be detectable. These results are not qualitatively inconsistent with recent theoretical and experimental investigations. Uncertainties in our knowledge of the fundamental vibration frequencies prevent more definite predictions.The use of Slater 3d atomic orbitals for vanadium leads to an unrealistically large increase in the tetrahedral deformation and distortion energy. But replacement of the purely atomic 3d orbital by a delocalized molecular orbital for the e electron leads to only a very small change (about 1 per cent) in the bond length difference between VCl4+ and VCl4.

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A double blind study on determination of ABO blood groups of 210 cholera patients, 44 diarrhoea cases due to Vibrio parahaemolyticus, and 148 diarrhoea cases from whom no vibrios could be isolated (control group), was conducted in Calcutta: A statistically significant difference was found in blood group ‘O’ when comparison was made between control and cholera groups. No significant association was, however, noticed between V. parahaemolyticus-induced diarrhoea and ABO blood group.

Vibrio cholerae serogroup O139 Bengal, a novel strain with epidemic potential, completely displaced V. cholerae serogroup 01 in Calcutta in January 1993, which was followed by an epidemic caused by V. cholerae O139 in March–May 1993. From November 1992 to July 1993, 95.6% of 916 V. cholerae isolates submitted to the National Institute of Cholera and Enteric Diseases from 28 locations in India were confirmed as serogroup O139. As of July 1993, V. cholerae O139 had been isolated from 13 Indian states and a union territory, and large outbreaks of cholera caused by the O139 serogroup had occurred in several cities. The extent of spread of V. cholerae O139 Bengal in India and its ability to swiftly disseminate leaves little doubt that this is the beginning of the eighth pandemic of cholera.

Reaction of the dithioacetals (I) with guanidine nitrate (II) in the presence of a base yields the pyrimidine derivatives (III).