Michel Caffarel

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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)
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)
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)
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)
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)
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)
We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is(More)
We present a modified definition of the Electron Pair Localization Function (EPLF), initially defined within the framework of quantum Monte Carlo approaches [ Scemama , A. ; Caffarel , M. ; Chaquin , P. J. Chem. Phys. 2004 , 121 , 1725 ] to be used in Density Functional Theories (DFT) and ab initio wave-function-based methods. This modified version of the(More)