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We present a general approach to greatly increase at little cost the efficiency of Monte Carlo algorithms. To each observable to be computed we associate a renormalized observable (improved estimator) having the same average but a different variance. By writing down the zero-variance condition a fundamental equation determining the optimal choice for the(More)
A simple and stable method for computing accurate expectation values of observable with Variational Monte Carlo (VMC) or Diffusion Monte Carlo (DMC) algorithms is presented. The basic idea consists in replacing the usual " bare " estimator associated with the observable by an improved or " renormalized " estimator. Using this estimator more accurate(More)
Although it would be tempting to associate the Lewis structures to the maxima of the squared wave function |Psi|2, we prefer in this paper the use of domains of the three-dimensional space, which maximize the probability of containing opposite-spin electron pairs. We find for simple systems (CH4, H2O, Ne, N2, C2H2) domains comparable to those obtained with(More)
Various strategies to implement efficiently quantum Monte Carlo (QMC) simulations for large chemical systems are presented. These include: (i) the introduction of an efficient algorithm to calculate the computationally expensive Slater matrices. This novel scheme is based on the use of the highly localized character of atomic Gaussian basis functions (not(More)
An algorithm to compute efficiently the first two derivatives of (very) large multideterminant wavefunctions for quantum Monte Carlo calculations is presented. The calculation of determinants and their derivatives is performed using the Sherman-Morrison formula for updating the inverse Slater matrix. An improved implementation based on the reduction of the(More)
The paper collects the answers of the authors to the following questions: What is the significance of topological approach? Can new chemical concepts be found by a topological approach? What is the status of a chemical concept within a topological approach? Should topological approaches provide measurable quantities? Is it possible to predict the outcome of(More)
Although potentially powerful, molecular oxygen is an inert oxidant due to the triplet nature of its ground state. Therefore, many enzymesse various metal cations (M) to produce singlet active species M(n) O(2) . In this communication we investigate the topology of the Electron Localization Function (ELF) within five biomimetic complexes which are(More)
Sujet : Analyse mathématique et numérique de modèles pour les matériaux, de l'échelle microscopique à l'échelle macroscopique soutenue le mercredi 3 juin 2009 devant le jury composé de Je termine par un grand merci à tous mes proches, et particulièrement à Marion et Jeanne sur qui je peux toujours compter pour me soutenir.
An alternative Monte Carlo estimator for the one-body density rho(r) is presented. This estimator has a simple form and can be readily used in any type of Monte Carlo simulation. Comparisons with the usual regularization of the delta-function on a grid show that the statistical errors are greatly reduced. Furthermore, our expression allows accurate(More)
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