Diffusion Monte Carlo study of electronic properties for H and Be atoms /

We examined three different algorithms used in diffusion Monte Carlo (DMC) to study their precisions and accuracies in predicting properties of isolated atoms, which are H atom ground state, Be atom ground state and H atom first excited state. All three algorithms — basic DMC, minimal stochastic reconfiguration DMC, and pure DMC, each with future-walking, are successfully impletmented in ground state energy and simple moments calculations with satisfactory results. Pure diffusion Monte Carlo with future-walking algorithm is proven to be the simplest approach with the least variance. Polarizabilities for Be atom ground state and H atom first excited state are not satisfactorily estimated in the infinitesimal differentiation approach. Likewise, an approach using the finite field approximation with an unperturbed wavefunction for the latter system also fails. However, accurate estimations for the a-polarizabilities are obtained by using wavefunctions that come from the time-independent perturbation theory. This suggests the flaw in our approach to polarizability estimation for these difficult cases rests with our having assumed the trial function is unaffected by infinitesimal perturbations in the Hamiltonian.

Comparative study of bovine heart and bacillus subtilis cytochrome c oxidase vesicles and the influence of bulk pH on cytochrome c oxidase components

Studies on the steady state behavior of soluble cytochrome c oxidase are extensive. These studies have examined the influence of ionic strength and pH and may provide answers to questions such as the link between proton translocation and charge separation. The present study examined the influence of external bulk pH on ApH formation, biphasic kinetics, and steady state reduction of cytochromes c and a of cytochrome c oxidase in proteoliposomes. Bulk pH has an appreciable effect on ApH formation and steady state reduction levels of cytochromes c and 8. Bulk pH affected total Vmax and Km at the low affinity binding site of cytochrome c. This study also examined the influence of bovine serum albumin and free fatty acids on proton pumping activity in bovine heart proteoliposomes. Proton pumping activity decreased after treatment with BSA, and was subsequently reinstated after further treatment with FFA. Much study in the superfamily of haem/copper oxidases has recently been devoted to the bacterial oxidases. The present study has examined some protein composition characteristics and bioenergetic features of Bacillus subtilis cytochrome caa3 oxidase. Results provide evidence for the structural composition of the enzyme in relation to the covalently bound cytochrome c to the oxidas~. Bioenergetically, caa3 COV showed appreciable proton pumping activity. Steady state analysis of the caa3 COV showed significantly different cytochrome c and a reduction characteristics compared to the bovine enzyme.

The diffusion of Co⠶溩 Zrâ â Tiâ â alloy /|nS. Kumar. -- 260 St Catharines [Ont.] : Dept. of Physics, Brock University,

The diffusion of Co60 in the body centered cubic beta phase of a ZrSOTi SO alloy has been studied at 900°, 1200°, and 1440°C. The results confirm earlier unpublished data obtained by Kidson17 • The temperature dependence of the diffusion coefficient is unusual and suggests that at least two and possibly three mechanisms may be operative Annealing of the specimen in the high B.C.C. region prior to the deposition of the tracer results in a large reduction in the diffusion coefficient. The possible significance of this effect is discussed in terms of rapid transport along dislocation network.

Exact property estimation from diffusion Monte Carlo with minimal stochastic reconfiguration /

Our objective is to develop a diffusion Monte Carlo (DMC) algorithm to estimate the exact expectation values, ($o|^|^o), of multiplicative operators, such as polarizabilities and high-order hyperpolarizabilities, for isolated atoms and molecules. The existing forward-walking pure diffusion Monte Carlo (FW-PDMC) algorithm which attempts this has a serious bias. On the other hand, the DMC algorithm with minimal stochastic reconfiguration provides unbiased estimates of the energies, but the expectation values ($o|^|^) are contaminated by ^, an user specified, approximate wave function, when A does not commute with the Hamiltonian. We modified the latter algorithm to obtain the exact expectation values for these operators, while at the same time eliminating the bias. To compare the efficiency of FW-PDMC and the modified DMC algorithms we calculated simple properties of the H atom, such as various functions of coordinates and polarizabilities. Using three non-exact wave functions, one of moderate quality and the others very crude, in each case the results are within statistical error of the exact values.