Anharmonic molecular mechanics: Ab initio based Morse parameterisations for the popular MM3 force field

Methodologies for creating reactive potential energy surfaces from molecular mechanics force-fields are becoming increasingly popular. To date, molecular mechanics force-fields use harmonic expressions to treat bonding stretches, which is a poor approximation in reactive molecular dynamics simulations since bonds are displaced significantly from their equilibrium positions. For such applications there is need for a better treatment of anharmonicity. In this contribution Morse bonding potentials have been extensively parameterised for the atom types in the MM3 force field of Allinger and co-workers using high level CCSD(T)(F12*) energies. To our knowledge this is the first instance of a large-scale paramerization of Morse potentials in a popular force field

Efficient and accurate evaluation of potential energy matrix elements for quantum dynamics using Gaussian process regression

Solution of the time-dependent Schro ̈dinger equation using a linear combination of basis functions, such as Gaussian wavepackets (GWPs), requires costly evaluation of integrals over the entire potential energy surface (PES) of the system. The standard approach, motivated by computational tractability for direct dynamics, is to approx- imate the PES with a second order Taylor expansion, for example centred at each GWP. In this Article, we propose an alternative method for approximating PES ma- trix elements based on PES interpolation using Gaussian process regression (GPR). Our GPR scheme requires only single-point evaluations of the PES at a limited num- ber of configurations in each time-step; the necessity of performing often-expensive evaluations of the Hessian matrix is completely avoided. In applications to 2-, 5- and 10-dimensional benchmark models describing a tunnelling coordinate coupled non-linearly to a set of harmonic oscillators, we find that our GPR method results in PES matrix elements for which the average error is, in the best case, two orders-of- magnitude smaller and, in the worst case, directly comparable to that determined by any other Taylor expansion method, without requiring additional PES evaluations or Hessian matrices. Given the computational simplicity of GPR, as well as the op- portunities for further refinement of the procedure highlighted herein, we argue that our GPR methodology should replace methods for evaluating PES matrix elements using Taylor expansions in quantum dynamics simulations

Witnessing eigenstates for quantum simulation of Hamiltonian spectra

The efficient calculation of Hamiltonian spectra, a problem often intractable on classical machines, can find application in many fields, from physics to chemistry. Here, we introduce the concept of an "eigenstate witness" and through it provide a new quantum approach which combines variational methods and phase estimation to approximate eigenvalues for both ground and excited states. This protocol is experimentally verified on a programmable silicon quantum photonic chip, a mass-manufacturable platform, which embeds entangled state generation, arbitrary controlled-unitary operations, and projective measurements. Both ground and excited states are experimentally found with fidelities >99%, and their eigenvalues are estimated with 32-bits of precision. We also investigate and discuss the scalability of the approach and study its performance through numerical simulations of more complex Hamiltonians. This result shows promising progress towards quantum chemistry on quantum computers.Comment: 9 pages, 4 figures, plus Supplementary Material [New version with minor typos corrected.

Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations

State-of-the-art ab initio techniques have been applied to compute the potential energy surface for the lithium atom interacting with the lithium hydride molecule in the Born–Oppenheimer approximation. The interaction potential was obtained using a combination of the explicitly correlated unrestricted coupled-cluster method with single, double, and noniterative triple excitations [UCCSD(T)-F12] for the core–core and core–valence correlation and full configuration interaction for the valence–valence correlation. The potential energy surface has a global minimum 8743 cm−1 deep if the Li–H bond length is held fixed at the monomer equilibrium distance or 8825 cm−1 deep if it is allowed to vary. In order to evaluate the performance of the conventional CCSD(T) approach, calculations were carried out using correlation-consistent polarized valence X-tuple-zeta basis sets, with X ranging from 2 to 5, and a very large set of bond functions. Using simple two-point extrapolations based on the single-power laws X−2 and X−3 for the orbital basis sets, we were able to reproduce the CCSD(T)–F12 results for the characteristic points of the potential with an error of 0.49% at worst. The contribution beyond the CCSD(T)–F12 model, obtained from full configuration interaction calculations for the valence–valence correlation, was shown to be very small, and the error bars on the potential were estimated. At linear LiH–Li geometries, the ground-state potential shows an avoided crossing with an ion-pair potential. The energy difference between the ground-state and excited-state potentials at the avoided crossing is only 94 cm−1. Using both adiabatic and diabatic pictures, we analyze the interaction between the two potential energy surfaces and its possible impact on the collisional dynamics. When the Li–H bond is allowed to vary, a seam of conical intersections appears at C2v geometries. At the linear LiH–Li geometry, the conical intersection is at a Li–H distance which is only slightly larger than the monomer equilibrium distance, but for nonlinear geometries it quickly shifts to Li–H distances that are well outside the classical turning points of the ground-state potential of LiH. This suggests that the conical intersection will have little impact on the dynamics of Li–LiH collisions at ultralow temperatures. Finally, the reaction channels for the exchange and insertion reactions are also analyzed and found to be unimportant for the dynamics

Oscillation mark formation in continuous casting

A mathematical model based on lubrication was used to study the formation of notches steel that is cast from a vertically oscillating mould. The analysis is a continuation of a problem that was presented at Heriot-Watt in 1988 and Oxford in 1989

Problem gambling: a suitable case for social work?

Problem gambling attracts little attention from health and social care agencies in the UK. Prevalence surveys suggest that 0.6% of the population are problem gamblers and it is suggested that for each of these individuals, 10–17 other people, including children and other family members, are affected. Problem gambling is linked to many individual and social problems including: depression, suicide, significant debt, bankruptcy, family conflict, domestic violence, neglect and maltreatment of children and offending. This makes the issue central to social work territory. Yet, the training of social workers in the UK has consistently neglected issues of addictive behaviour. Whilst some attention has been paid in recent years to substance abuse issues, there has remained a silence in relation to gambling problems. Social workers provide more help for problems relating to addictions than other helping professions. There is good evidence that treatment, and early intervention for gambling problems, including psycho-social and public health approaches, can be very effective. This paper argues that problem gambling should be moved onto the radar of the social work profession, via inclusion on qualifying and post-qualifying training programmes and via research and dissemination of good practice via institutions such as the Social Care Institute for Excellence (SCIE). Keywords: problem gambling; addictive behaviour; socia

The effects of periodontal therapy on serum antibody (IgG) levels to plaque microorganisms *

The influence of periodontal therapy on serum antibody titers to selected periodontal disease-associated microorganisms was assessed in 23 patients having chronic inflammatory periodontal disease (CIPD), The immunoglobulin G (IgG) titers were dÉtÉrmined by the micro ELISA technique in serum samples obtained prior to treatment; following a hygienic phase which included scaling, root planing, and oral hygiene instruction; following surgical treatment; and one year and two years following hygienic phase (maintenance phase). Considerable individual variability existed in the magnitude of immune response to specific bacterial preparations. Significant reductions in the mean antibody titers were seen to A. viscosus. S. sanguis. F. nucleatum, S, spuligena, B. gingivalis. B. interme-dius. B. melaninogeniem, T. vincentii , and T denticola by the end of the second year of maintenance. There was no consistent response to Capnucytophaga. When individual patient responses were examined. 6 of the 23 were found to have elevated titers to at least one of the microorganisms in the interval between pretreatment and the end of the hygienic phase; however, in all but one case, the titers at the end of the second year of maintenance were below pretreatment levels. Antibody levels to bacteria such as S. sanguis were modified during therapy. This would indicate that immune responses to microbes not generally considered to be “periodontal pathogens” may be modified by adjuvant activity associated with subgingival plaque or changes in the environment of the sulcus and that subsequent changes in titer do not necessarily reflect a role of that microorganism in the disease process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75110/1/j.1600-051X.1988.tb02127.x.pd