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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)

- Anthony Scemama, Michel Caffarel, Andreas Savin
- Journal of Computational Chemistry
- 2007

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)

- Anthony Scemama, Michel Caffarel, Emmanuel Oseret, William Jalby
- Journal of Computational Chemistry
- 2013

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)

- Anthony Scemama, Michel Caffarel, Emmanuel Oseret, William Jalby
- VECPAR
- 2012

- Aurélien de la Lande, Dennis R. Salahub, +6 authors Jean-Philip Piquemal
- Journal of Computational Chemistry
- 2011

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)

- Paul L. Ayers, Russell J. Boyd, +16 authors Bernard Silvi
- 2014

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)

- Anthony Scemama, Thomas Applencourt, Emmanuel Giner, Michel Caffarel
- Journal of Computational Chemistry
- 2016

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)

- Benoît Braïda, Julien Toulouse, Michel Caffarel, C J Umrigar
- The Journal of chemical physics
- 2011

We consider the use in quantum Monte Carlo calculations of two types of valence bond wave functions based on strictly localized active orbitals, namely valence bond self-consistent-field and breathing-orbital valence bond wave functions. Complemented by a Jastrow factor, these Jastrow-valence-bond wave functions are tested by computing the equilibrium well… (More)

- Roland Assaraf, Michel Caffarel, Anthony Scemama
- Physical review. E, Statistical, nonlinear, and…
- 2007

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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