A5062574809- Advanced Chemical Physics Studies
- Spectroscopy and Quantum Chemical Studies
- Quantum, superfluid, helium dynamics
- Physics of Superconductivity and Magnetism
- Catalysis and Oxidation Reactions
- Catalytic Processes in Materials Science
- Machine Learning in Materials Science
- Theoretical and Computational Physics
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum and electron transport phenomena
- Linguistics and Discourse Analysis
- Electron and X-Ray Spectroscopy Techniques
- Syntax, Semantics, Linguistic Variation
- Advanced Physical and Chemical Molecular Interactions
- Atomic and Subatomic Physics Research
- Advanced NMR Techniques and Applications
- Quantum many-body systems
- History and advancements in chemistry
- Linguistic Variation and Morphology
- Magnetism in coordination complexes
- Free Radicals and Antioxidants
- X-ray Diffraction in Crystallography
- Historical Linguistics and Language Studies
- Nonlinear Photonic Systems
- Quantum Electrodynamics and Casimir Effect
Laboratoire de Chimie et Physique Quantiques
2016-2025
Université Toulouse III - Paul Sabatier
2014-2025
Université de Toulouse
2015-2024
Centre National de la Recherche Scientifique
2015-2024
University of Ferrara
2016
Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes
1993-2015
The University of Sydney
1992-2012
Laboratoire de Photonique Quantique et Moléculaire
2010
Sorbonne Université
1993-2004
Laboratoire de Chimie Théorique
1996-2004
We present a powerful method for calculating the thermodynamic properties of infinite-dimensional Hubbard-type models using an exact diagonalization Anderson model with finite number sites. The resolution obtained Green's functions is far superior to that quantum Monte Carlo calculations. apply half-filled Hubbard discussion metal-insulator transition, and two-band where we find direct evidence existence superconducting instability at low temperatures.
Striving to define very accurate vertical transition energies, we perform both high-level coupled cluster (CC) calculations (up CCSDTQP) and selected configuration interaction (sCI) several millions of determinants) for 18 small compounds (water, hydrogen sulfide, ammonia, chloride, dinitrogen, carbon monoxide, acetylene, ethylene, formaldehyde, methanimine, thioformaldehyde, acetaldehyde, cyclopropene, diazomethane, formamide, ketene, nitrosomethane, the smallest streptocyanine). By...
Excited states exhibiting double excitation character are notoriously difficult to model using conventional single-reference methods, such as adiabatic time-dependent density-functional theory (TD-DFT) or equation-of-motion coupled cluster (EOM-CC). In the present work, we provide accurate reference energies for transitions involving a substantial amount of series increasingly large diffuse-containing atomic basis sets. Our set gathers 20 vertical from 14 small- and medium-size molecule....
We study a model of strongly interacting lattice bosons with Gutzwiller-type wave function that contains only on-site correlations. The variational energy and the condensate fraction associated are exactly evaluated for both finite infinite systems compared exact quantum Monte Carlo results in two dimensions. This ansatz gives correct qualitative picture phase diagram this system; at commensurate densities, system enters Mott-insulator large values interaction.
Defining accurate and compact trial wavefunctions leading to small statistical fixed-node errors in quantum Monte Carlo (QMC) calculations is still a challenging problem. Here we propose make use of selected configuration interaction (CI) expansions obtained by selecting the most important determinants through perturbative criterion. A major advantage with respect truncated CASSCF or CI limited maximum number excitations (e.g, CISD) that much smaller can be considered (many unessential are...
Quantum chemistry is a discipline which relies heavily on very expensive numerical computations. The scaling of correlated wave function methods lies, in their standard implementation, between O(N5) and O(eN) , where N proportional to the system size. Therefore, performing accurate calculations chemically meaningful systems requires (i) approximations that can lower computational (ii) efficient implementations take advantage modern massively parallel architectures. Package an open-source...
Selected configuration interaction (sCI) methods including second-order perturbative corrections provide near full CI (FCI) quality energies with only a small fraction of the determinants FCI space. Here, we introduce both state-specific and multi-state sCI method based on using selection made iteratively (CIPSI) algorithm. The present revises reference (internal) space under effect its outer via construction an effective Hamiltonian, following shifted-Bk philosophy Davidson co-workers. In...
A hybrid stochastic-deterministic approach for computing the second-order perturbative contribution E(2) within multireference perturbation theory (MRPT) is presented. The idea at heart of our scheme—based on a reformulation as sum elementary contributions associated with each determinant MR wave function—is to split into stochastic and deterministic part. During simulation, part gradually reduced by dynamically increasing until one reaches desired accuracy. In sharp contrast purely Monte...
We present a general approach to greatly increase at little cost the efficiency of Monte Carlo algorithms. To each observable be computed we associate renormalized (improved estimator) having same average but different variance. By writing down zero-variance condition fundamental equation determining optimal choice for is derived (zero-variance principle separately). show, with several examples including classical and quantum calculations, that method can very powerful.
The potential energy curve of the F$_2$ molecule is calculated with Fixed-Node Diffusion Monte Carlo (FN-DMC) using Configuration Interaction (CI)-type trial wavefunctions. To keep number determinants reasonable (the first and second derivatives wavefunction need to be at each step FN-DMC), CI expansion restricted those that contribute most total energy. selection made so-called CIPSI approach (Configuration a Perturbative Selection Iteratively). Quite remarkably, nodes wavefunctions are...
The pair coupled cluster doubles (pCCD) method (where the excitation manifold is restricted to electron pairs) has a series of interesting features. Among others, it provides ground-state energies very close what obtained with doubly occupied configuration interaction (DOCI), but polynomial cost (compared exponential latter). Here, we address whether this similarity holds for excited states by exploring symmetric dissociation linear H
A simple and stable method for computing accurate expectation values of observable with Variational Monte Carlo (VMC) or Diffusion (DMC) algorithms is presented. The basic idea consists in replacing the usual ``bare'' estimator associated by an improved ``renormalized'' estimator. Using this more averages are obtained: Not only statistical fluctuations reduced but also systematic error (bias) approximate VMC (fixed-node) DMC probability densities. It shown that estimators obey a...
This paper presents systematic developments in the previously initiated line of research concerning a quantum Monte Carlo (QMC) method based on use pure diffusion process corresponding to some reference function and generalized Feynman–Kac path integral formalism. Not only mean values observables, but also response properties are expressed using suitable integrals involving measure process. Moreover, by relying ergodic character this process, may be evaluated as time-averages along any...
All-electron Fixed-node Diffusion Monte Carlo calculations for the nonrelativistic ground-state energy of water molecule at equilibrium geometry are presented. The determinantal part trial wavefunction is obtained from a selected Configuration Interaction calculation [Configuration using Perturbative Selection done Iteratively (CIPSI) method] including up to about 1.4 × 106 determinants. Calculations made cc-pCVnZ family basis sets, with n = 2 5. In contrast most quantum works no...
In diffusion Monte Carlo (DMC) methods, the nodes (or zeroes) of trial wave function dictate magnitude fixed-node (FN) error. standard DMC implementations, are optimized by stochastically optimizing a short multideterminant expansion in presence an explicitly correlated Jastrow factor. Here, following recent proposal, we pursue different route and consider selected configuration interaction (sCI) expansions built with CIPSI (Configuration Interaction using Perturbative Selection made...
Quantum Monte Carlo (QMC) is a stochastic method that has been particularly successful for ground-state electronic structure calculations but mostly unexplored the computation of excited-state energies. Here, we show within Jastrow-free QMC protocol relying on deterministic and systematic construction nodal surfaces using selected configuration interaction (sCI) expansions, one able to obtain accurate excitation energies at fixed-node diffusion (FN-DMC) level. This evidences errors in ground...
We report ground- and excited-state dipole moments oscillator strengths (computed in different "gauges" or representations) of full configuration interaction (FCI) quality using the selected method known as Configuration Interaction a Perturbative Selection made Iteratively (CIPSI). Thanks to set encompassing 35 properties computed 11 small molecules, present near-FCI estimates allow us assess accuracy high-order coupled-cluster (CC) calculations including up quadruple excitations. In...
We investigate the metal-insulator transition of one-dimensional $\mathrm{SU}(N)$ Hubbard model for repulsive interaction. Using bosonization approach a Mott in charge sector at half filling ${(k}_{F}=\ensuremath{\pi}{/Na}_{0})$ is conjectured $N>2.$ Expressions and spin velocities as well Luttinger-liquid parameters some correlation functions are given. The theoretical predictions compared with numerical results obtained an improved zero-temperature quantum Monte Carlo approach. method used...
We present a simple and stable quantum Monte Carlo approach for computing forces between atoms in molecule. In this we propose to use as estimator of the force standard Hellmann–Feynman expression (local expressed derivative total potential energy with respect internuclear coordinates). Invoking recently introduced zero-variance principle it is shown how infinite variance associated can be made finite by introducing some suitably renormalized force. Practical calculations molecules H2, Li2,...
In this paper we discuss various aspects of diffusion Monte Carlo methods using a fixed number walkers. First, rigorous proof the divergence pure (PDMC) (DMC without branching in which weights are carried along trajectories) is given. Second, bias-free method combining DMC and PDMC approaches, based on minimal stochastic reconfiguration population, discussed. Finally, some illustrative calculations for system coupled quantum rotators presented.
We present a comparative study of the spatial distribution spin density ground state CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number studies have shown that an accurate description electronic structure lowest-lying states this molecule is particularly challenging due to interplay between strong dynamical correlation effects in 3d shell delocalization hole over chlorine atoms. More generally, problem...