Fortran 90 implementation of the Hartree-Fock approach within the CNDO/2 and INDO models

Despite the tremendous advances made by the ab initio theory of electronic structure of atoms and molecules, its applications are still not possible for very large systems. Therefore, semi-empirical model Hamiltonians based on the zero-differential overlap (ZDO) approach such as the Pariser-Parr-Pople, CNDO, INDO, etc. provide attractive, and computationally tractable, alternatives to the ab initio treatment of large systems. In this paper we describe a Fortran 90 computer program developed by us, that uses CNDO/2 and INDO methods to solve Hartree-Fock(HF) equation for molecular systems. The INDO method can be used for the molecules containing the first-row atoms, while the CNDO/2 method is applicable to those containing both the first-, and the second-row, atoms. We have paid particular attention to computational efficiency while developing the code, and, therefore, it allows us to perform calculations on large molecules such as C_60 on small computers within a matter of seconds. Besides being able to compute the molecular orbitals and total energies, our code is also able to compute properties such as the electric dipole moment, Mulliken population analysis, and linear optical absorption spectrum of the system. We also demonstrate how the program can be used to compute the total energy per unit cell of a polymer. The applications presented in this paper include small organic and inorganic molecules, fullerene C_60, and model polymeric systems, viz., chains containing alternating boron and nitrogen atoms (BN chain), and carbon atoms (C chain).Comment: 29 pages, 3 figures, to appear in Computer Physics Communication

Ehlers Transformations and String Effective Action

We explicitly obtain the generalization of the Ehlers transformation for stationary axisymmetric Einstein equations to string theory. This is accomplished by finding the twist potential corresponding to the moduli fields in the effective two dimensional theory. Twist potential and symmetric moduli are shown to transform under an $O(d,d)$ which is a manifest symmetry of the equations of motion. The non-trivial action of this $O(d,d)$ is given by the Ehlers transformation and belongs to the set $O(d) \times O(d)\over O(d)$.Comment: 13 pages, minor corrections, version to appear in Physics Letters B35

Symmetries of Heterotic String Theory

We study the symmetries of the two dimensional Heterotic string theory by following the approach of Kinnersley et al for the study of stationary-axially symmetric Einstein-Maxwell equations. We identify the finite dimensional groups $G'$ and $H'$ for the Einstein-Maxwell equations. We also give the constructions for the infinite number of conserved currents and the affine $\hat{o}(8, 24)$ symmetry algebra in this formulation. The generalized Ehlers and Harrison transformations are identified and a parallel between the infinite dimensional symmetry algebra for the heterotic string case with $\hat{sl}(3, R)$ that arise in the case of Einstein-Maxwell equations is pointed out.Comment: 26 pages, Few comments added, version to appear in Nuclear Physics

Thermodynamics of Two Dimensional Black Holes

Thermodynamic relations for a class of 2D black holes are obtained corresponding to observations made from finite spatial distances. We also study the thermodynamics of the charged version of the Jackiw-Teitelboim black holes found recently by Lowe and Strominger. Our results corroborate, in appropriate limits, to those obtained previously by other methods. We also analyze the stability of these black holes thermodynamically.Comment: 18 pages (One uncoded postscript file for figure appended), IP/BBSR/94-5

Entropy of Extremal Black Holes in Two Dimensions

Entropy for two dimensional extremal black holes is computed explicitly in a finite-space formulation of the black hole thermodynamics and is shown to be zero {\it locally}. Our results are in conformity with the recent one by Hawking et al in four dimensions.Comment: 11 page

Specialization, Integration, and Multi-sourcing: A study of Large IT Outsourcing Projects

IT outsourcing has three broad forms: (i) Single-Sourcing, where the client outsources to one primary vendor, (ii) Single-Sourcing with subcontracting , where the primary vendor involves other/secondary vendors in the project, and (iii) Multi-Sourcing, where the client outsources to multiple primary vendors. Using a dataset of large IT outsourcing contracts from the SCD database with 22,031 large IT outsourcing contracts from 1989-2009 we examine the antecedents of choice with respect to the form of outsourcing arrangements that firms have. Our results indicate that higher value projects are more likely to be single-sourced with subcontracting; however, a highly modularized project is more likely to be multi-sourced. Further, client and vendor experience dictate whether multi-sourcing or single-sourcing is chosen due to tradeoffs involved in benefits from specialization in one case versus the cost of coordination in the other. Finally, as the IT outsourcing industry matures, single-sourcing with subcontracting and multi-sourcing increase

Neutrino Masses and a Fourth Generation of Fermions

We study neutrino mass generation in models with four chiral families of leptons and quarks and four right handed neutrinos. Generically, in these models there are three different contributions to the light neutrino masses: the usual see-saw contribution, the tree-level contribution due to mixing of light neutrinos with neutrino of the fourth generation, and the two loop contribution due to the Majorana mass term of the fourth neutrino. We study properties of these contributions and their experimental bounds. The regions of the parameters (mixings of the fourth neutrino, masses of RH neutrino components, etc.) have been identified where various contributions dominate. New possibilities of a realization of the flavour symmetries in the four family context are explored. In particular, we consider applications of the smallest groups, e.g. SG(20,3), with irreducible representation 4.Comment: 33 pages, 4 figures; Eq. (18) corrected and thus corrections to Eqs. (21,26-28,41,42,44-46) and figures, the loop contribution reduced by 2 orders of magnitude; general conclusions unchanged; accepted by Nucl. Phys.