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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 averages… (More)

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)

Using a collective-mode Monte Carlo method (the Wolff-Swendsen-Wang algorithm), we compute the spin-stiffness of the two-dimensional classical Heisenberg model. We show that it is the relevant physical quantity to investigate the behaviour of the model in the very low temperature range inaccessible to previous studies based on correlation length and… (More)

- Srimanta Pakhira, Benjamin S Lengeling, Olayinka A Olatunji-Ojo, Michel Caffarel, Michael Frenklach, William A. Lester
- The journal of physical chemistry. A
- 2015

To assist understanding of combustion processes, we have investigated reactions of methylidyne (CH) with acrolein (CH2CHCHO) using the quantum Monte Carlo (QMC) and other computational methods. We present a theoretical study of the major reactions reported in a recent experiment on the subject system. Both DFT and MP2 computations are carried out, and the… (More)

- Anthony Scemama, Tony Lelièvre, Gabriel Stoltz, Eric Cancès, Michel Caffarel
- The Journal of chemical physics
- 2006

We propose a new algorithm for sampling the N-body density mid R:Psi(R)mid R:(2)R(3N)mid R:Psimid R:(2) in the variational Monte Carlo framework. This algorithm is based upon a modified Ricci-Ciccotti discretization of the Langevin dynamics in the phase space (R,P) improved by a Metropolis-Hastings accept/reject step. We show through some representative… (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, 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
- VECPAR
- 2012

In this work we discuss several key aspects for an efficient implementation and deployment of large-scale quantum Monte Carlo (QMC) simulations for chemical applications on petaflops infrastructures. Such aspects have been implemented in the QMC=Chem code developed at Toulouse (France). First, a simple, general, and fault-tolerant simulation environment… (More)

- Anthony Scemama, Patrick Chaquin, Michel Caffarel
- The Journal of chemical physics
- 2004

In this work we introduce an electron localization function describing the pairing of electrons in a molecular system. This function, called "electron pair localization function," is constructed to be particularly simple to evaluate within a quantum Monte Carlo framework. Two major advantages of this function are the following: (i) the simplicity and… (More)

- Anthony Scemama, Thomas Applencourt, Emmanuel Giner, Michel Caffarel
- The Journal of chemical physics
- 2014

We present accurate nonrelativistic ground-state energies of the transition metal atoms of the 3d series calculated with Fixed-Node Diffusion Monte Carlo (FN-DMC). Selected multi-determinantal expansions obtained with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) method and including the most prominent determinants of… (More)