Linearized Coupled Cluster Correction on the Antisymmetric Product of 1 reference orbital Geminals

We present a Linearized Coupled Cluster (LCC) correction based on an Antisymmetric Product of 1 reference orbital Geminals (AP1roG) reference state. In our LCC ansatz, the cluster operator is restricted to double and to single and double excitations as in standard single-reference CC theory. The performance of the AP1roG-LCC models is tested for the dissociation of diatomic molecules (C$_2$ and F$_2$), spectroscopic constants of the uranyl cation (UO$_2^{2+}$), and the symmetric dissociation of the H$_{50}$ hydrogen chain. Our study indicates that an LCC correction based on an AP1roG reference function is more robust and reliable than corrections based on perturbation theory, yielding spectroscopic constants that are in very good agreement with theoretical reference data.Comment: 9 pages, 4 figure

A simple algorithm for the Kohn-Sham inversion problem applicable to general target densities

A simple algorithm for the Kohn-Sham inversion problem is presented. The method is found to converge toward a nearby v-representable Kohn-Sham density irrespective of the fact whether the initial target density has been v-representable or not. For the proposed procedure, the target density can be of general nature. The algorithm can handle Hartree-Fock and post-Hartree-Fock, spin-unpolarized and polarized states equally well. Additionally, experimental densities and even general gedanken densities can be treated. The algorithm is easy to implement and does not require an additional procedure to adjust eigenvalues

CheMPS2: a free open-source spin-adapted implementation of the density matrix renormalization group for ab initio quantum chemistry

The density matrix renormalization group (DMRG) has become an indispensable numerical tool to find exact eigenstates of finite-size quantum systems with strong correlation. In the fields of condensed matter, nuclear structure and molecular electronic structure, it has significantly extended the system sizes that can be handled compared to full configuration interaction, without losing numerical accuracy. For quantum chemistry (QC), the most efficient implementations of DMRG require the incorporation of particle number, spin and point group symmetries in the underlying matrix product state (MPS) ansatz, as well as the use of so-called complementary operators. The symmetries introduce a sparse block structure in the MPS ansatz and in the intermediary contracted tensors. If a symmetry is non-abelian, the Wigner-Eckart theorem allows to factorize a tensor into a Clebsch-Gordan coefficient and a reduced tensor. In addition, the fermion signs have to be carefully tracked. Because of these challenges, implementing DMRG efficiently for QC is not straightforward. Efficient and freely available implementations are therefore highly desired. In this work we present CheMPS2, our free open-source spin-adapted implementation of DMRG for ab initio QC. Around CheMPS2, we have implemented the augmented Hessian Newton-Raphson complete active space self-consistent field method, with exact Hessian. The bond dissociation curves of the 12 lowest states of the carbon dimer were obtained at the DMRG(28 orbitals, 12 electrons, D$_{\mathsf{SU(2)}}$=2500)/cc-pVDZ level of theory. The contribution of $1s$ core correlation to the $X^1\Sigma_g^+$ bond dissociation curve of the carbon dimer was estimated by comparing energies at the DMRG(36o, 12e, D$_{\mathsf{SU(2)}}$=2500)/cc-pCVDZ and DMRG-SCF(34o, 8e, D$_{\mathsf{SU(2)}}$=2500)/cc-pCVDZ levels of theory.Comment: 16 pages, 13 figure

Robust methods for predicting the transition states of chemical reactions: new approaches that focus on key coordinates

A new method for optimizing transition state and minima structures using redundant internal coordinates is presented. The new method is innovative because it allows the user to select a few key reduced coordinates, whose Hessian components will be accurately computed by finite differencing; the remaining elements of the Hessian are approximated with a quasi-Newton method. Usually the reduced coordinates are the coordinates that are involved in bond breaking/forming. In order to develop this method, several other innovations were made, including ways to (a) select the key reduced coordinates automatically, (b) guess the transition state quickly and efficiently, (c) choose dihedrals so that the “linear angle problem” is avoided, (d) robustly convert redundant internal coordinates to Cartesian coordinates. These, and other technical developments (e.g., new quasi-Newton Hessians, new trust-radius updates), were validated using a database of 7000 initial transition-state guesses for a diverse set of 140 chemical reactions

An Analysis of Faculty and Administrator Perceptions of Faculty Involvement in Decision-making in the University of Kentucky Community College System

The problem of this study was to determine if there is a significant difference between expressed perceptions of selected community college faculty and administrators concerning the extent to which faculty actually are involved in decision making and the extent to which they ought to be involved in decision making. This was a descriptive study, which utilized a survey methodology. Faculty and administrator perceptions were studied in six decisional areas: appointment, promotion and tenure decisions, academic decisions, administration, student affairs and advisement, system/state control, and general (overall faculty involvement). The study was conducted in the University of Kentucky Community College System, made up of fourteen 2-year institutions. The statistical analysis of data for hypotheses 1-12 warranted the following conclusions: (1) Faculty want to be involved more in all aspects of decision making; this desire is greatest among instructors and assistant professors. (2) Administrators want faculty to be involved more in decision making, although the desire is not as great among directors, associate directors, and assistant directors as it is with division chairs. (3) The variable of sex has little influence on perceptions of faculty and administrators concerning faculty involvement in decision making. (4) The decisional area where faculty exhibit the least decisional deprivation is Academic Decisions, indicating that they have greatest involvement with activities related to instruction. (5) Faculty and administrators are less satisfied with faculty involvement in System/State Control than in any other decisional area

Extended Hirshfeld: atomic charges that combine accurate electrostatics with transferability

C

The Military Establishment and Social Welfare: Past, Present (and Future?)

As we move toward the decade of the eighties we are becoming increasingly aware of the difficulties and realities of economics on a national level. More and more we, as a people, are faced with difficult choices concerning the services that we either demand of our government or which government deems it necessary to provide. Although it is an oversimplication, our Constitution mandates that government always follow to some degree a guns and (not or) butter philosophy in its preamble provisions dealing with common defense and general welfare. We have though paid dearly, in economic terms, for attempting to follow such a fatal guns and butter philosophy during the Vietnam conflict. Faced with the untenability of the above non-choice planners, elected officials, and others must take a hard look at current and future allocation of resources in order to maintain some semblance of living within our means. It is the purpose of this article to examine one area in which there could be a re-distribution of financial resources and to advance suggestions concerning the implementation of programs

A Hermit\u27s Tale

Senior Project submitted to The Division of Languages and Literature of Bard College