Pierre-Francois Loos

Connection between $GW$ and Extended Coupled Cluster Coupled-cluster (CC) theory and Green's function many-body perturbation theory (MBPT) have long evolved as distinct yet complementary frameworks for describing electronic correlation. While CC methods...

arxiv.org/abs/2602.10887 #compchem

Connections between Richardson–Gaudin states, perfect-pairing, and pair coupled-cluster theory Slater determinants underpin most electronic structure methods, but orbital-based approaches often struggle to describe strong correlation efficiently. Geminal-

Work with @titouloos.bsky.social @marm314.bsky.social :
PP is an independent pair model with a reference Hamiltonian. The corresponding PT2 correction \approx pCCD.

Here, seniority-zero correction only in the valence. The real correction coming soon.

Parquet theory for molecular systems: Formalism and static kernel parquet approximation The GW approximation has become a method of choice for predicting quasiparticle properties in solids and large molecular systems, owing to its favorable accurac

Parquet theory for molecular systems: Formalism and static kernel parquet approximation pubs.aip.org/aip/jcp/arti... #compchem

Complex Absorbing Potential Green’s Function Methods for Resonances The complex absorbing potential (CAP) formalism has been successfully employed in various wave function-based methods to study electronic resonance states. In contrast, Green’s function-based methods ...

Complex Absorbing Potential Green’s Function Methods for Resonances | Journal of Chemical Theory and Computation pubs.acs.org/doi/10.1021/... #compchem

Analytic $G_0W_0$ gradients based on a double-similarity transformation equation-of-motion coupled-cluster treatment The accurate prediction of ionization potentials (IPs) is central to understanding molecular reactivity, redox behavior, and spectroscopic properties. While vertical IPs can be accessed directly from ...

arxiv.org/abs/2510.23275 #compchem

Fully Analytic Nuclear Gradients for the Bethe–Salpeter Equation The Bethe–Salpeter equation (BSE) formalism, combined with the GW approximation for ionization energies and electron affinities, is emerging as an efficient and accurate method for predicting optical excitations in molecules. In this Letter, we present the first derivation and implementation of fully analytic nuclear gradients for the BSE@G0W0 method. Building on recent developments for G0W0 nuclear gradients, we derive analytic nuclear gradients for several BSE@G0W0 variants. We validate our implementation against numerical gradients and compare excited-state geometries and adiabatic excitation energies obtained from different BSE@G0W0 variants with those from state-of-the-art wave function methods.

Fully Analytic Nuclear Gradients for the Bethe–Salpeter Equation | The Journal of Physical Chemistry Letters pubs.acs.org/doi/10.1021/... #compchem

Connections between Richardson-Gaudin States, Perfect-Pairing, and Pair Coupled-Cluster Theory Slater determinants underpin most electronic structure methods, but orbital-based approaches often struggle to describe strong correlation efficiently. Geminal-based theories, by contrast, naturally c...

arxiv.org/abs/2510.06144 Exploring the "Connections between Richardson-Gaudin States, Perfect-Pairing, and Pair Coupled-Cluster Theory." #compchem @titouloos.bsky.social @johnsontheochem.bsky.social

Connections between Richardson-Gaudin States, Perfect-Pairing, and Pair Coupled-Cluster Theory Slater determinants underpin most electronic structure methods, but orbital-based approaches often struggle to describe strong correlation efficiently. Geminal-based theories, by contrast, naturally c...

arxiv.org/abs/2510.06144 #compchem

Parquet theory for molecular systems. I. Formalism and static kernel parquet approximation The $GW$ approximation has become a method of choice for predicting quasiparticle properties in solids and large molecular systems, owing to its favorable accuracy-cost balance. However, its accuracy ...

arxiv.org/abs/2509.03253 #compchem

QUEST Database of Highly-Accurate Excitation Energies We report theoretical best estimates of vertical transition energies (VTEs) for a large number of excited states and molecules: the quest database. This database includes 1489 aug-cc-pVTZ VTEs (731 singlets, 233 doublets, 461 triplets, and 64 quartets) for both valence and Rydberg transitions occurring in molecules containing from 1 to 16 non-hydrogen atoms. Quest also includes a significant list of VTEs for states characterized by a partial or genuine double-excitation character, known to be particularly challenging for many computational methods. The vast majority of the reported values are deemed chemically accurate, that is, are within ±0.05 eV of the FCI/aug-cc-pVTZ estimate. This allows for a balanced assessment of the performance of popular excited-state methodologies. We report the results of such benchmarks for various single- and multireference wave function approaches, and provide extensive Supporting Information allowing testing of other models. All corresponding data associated with the quest database, along with analysis tools, can be found in the associated GitHub repository at the following URL: https://github.com/pfloos/QUESTDB.

QUEST Database of Highly-Accurate Excitation Energies | Journal of Chemical Theory and Computation pubs.acs.org/doi/10.1021/... #compchem

Complex Absorbing Potential Green's Function Methods for Resonances The complex absorbing potential (CAP) formalism has been successfully employed in various wavefunction-based methods to study electronic resonance states. In contrast, Green's function-based methods a...

arxiv.org/abs/2507.03496 #compchem

Mostly for Johannes… He has done all the hard work.

Fully Analytic Nuclear Gradients for the Bethe--Salpeter Equation The Bethe-Salpeter equation (BSE) formalism, combined with the $GW$ approximation for ionization energies and electron affinities, is emerging as an efficient and accurate method for predicting optica...

arxiv.org/abs/2507.02160 #compchem

The QUEST Database of Highly-Accurate Excitation Energies We report theoretical best estimates of vertical transition energies (VTEs) for a large number of excited states and molecules: the \textsc{quest} database. This database includes 1489 \emph{aug}-cc-p...

🦣 update of #QUESTDB (Database of Highly-Accurate Excitation Energies) 🦖 The latest #preprint on #QUESTDB is just out on @arXiv (arxiv.org/abs/2506.11590) with the corresponding @github repo (github.com/pfloos/QUESTDB) where we have compiled all the data in various formats. Please share! #compchem

Richardson-Gaudin states of non-zero seniority II: Single-reference treatment of strong correlation Strongly correlated systems are well described as a configuration interaction of Slater determinants classified by their number of unpaired electrons. This treatment is however unfeasible. In this man...

Very short follow-up after the ridiculous part I. Short excitation-based CI of RG states converges quickly.

(ordinarily, I'd reply to a post from @titouloos.bsky.social )

arxiv.org/abs/2506.09379

Pesticides, mégabassines, élevages géants : la macronie plombe l’écologie. La une de Libération du lundi 26 mai 2025.

Pesticides, mégabassines, élevages géants : la macronie plombe l’écologie. C’est la une de Libération lundi.

Pour favoriser l’adoption d’une ­proposition de loi réclamée par la FNSEA, le camp présidentiel et LR s’apprêtent à empêcher les ­débats à l’Assemblée.

Potentially, yes.

Great question… you might be able to do QMC with a trial wave function that contains a determinant of plane waves with non-Aufbau filling. One would have to be extremely careful in the extrapolation process though as one has to make sure to use the same value of Δ for all finite-electron systems…

Excited states of the uniform electron gas The uniform electron gas (UEG) is a cornerstone of density-functional theory (DFT) and the foundation of the local-density approximation, one of the most succes

Excited states of the uniform electron gas pubs.aip.org/aip/jcp/arti...

Thank you for coming! ☀️

Comparing Perturbative and Commutator-Rank-Based Truncation Schemes in Unitary Coupled-Cluster Theory Unitary coupled cluster (UCC) theory offers a promising Hermitian alternative to conventional coupled cluster (CC) theory, but its practical implementation is hindered by the non-truncating nature of ...

arxiv.org/abs/2503.00617 #compchem

Driven similarity renormalization group with a large active space: Applications to oligoacenes, zeaxanthin, and chromium dimer We present a new implementation of the driven similarity renormalization group (DSRG) based on a density matrix renormalization group (DMRG) reference. The explicit build of high-order reduced density...

arxiv.org/abs/2503.01299 #compchem

Using Matrix-Free Tensor-Network Optimizations to Construct a Reduced-Scaling and Robust Second-Order Møller-Plesset Theory We investigate the application of the canonical polyadic decomposition (CPD) to the tensor hypercontraction (THC) and Laplace transform (LT) approximated second-order Møller-Plesset (MP2) method. By i...

arxiv.org/abs/2502.17683 #compchem

A Guide to Molecular Properties from the Bethe-Salpeter Equation The Bethe-Salpeter equation (BSE) combined with the Green's function GW method has successfully transformed into a robust computational tool to describe light-matter interactions and excitation spectr...

arxiv.org/abs/2502.08753 #compchem

The Conundrum of Diffuse Basis Sets: A Blessing for Accuracy yet a Curse for Sparsity Diffuse atomic orbital basis sets have proven to be essential to obtain accurate interaction energies, especially in regard to non-covalent interactions. However, they also have a detrimental impact o...

arxiv.org/abs/2502.04631 #compchem

Simple and efficient computational strategies for calculating orbital energies and pair-orbital energies from pCCD-based methods We introduce affordable computational strategies for calculating orbital and pair-orbital energies in atomic and molecular systems. Our methods are based on the pair Coupled Cluster Doubles (pCCD) ans...

arxiv.org/abs/2502.03098 #compchem

New model for the excited states of the uniform electron gas (kinetic, exchange & leading term of correlation). Hopefully, useful to construct state-specific density-functional approximations for excited states. 🌻Comments welcome! 🌺@LCPQ_UMR5626 @pterosor #compchem #UEG #DFT

Excited States of the Uniform Electron Gas The uniform electron gas (UEG) is a cornerstone of density-functional theory (DFT) and the foundation of the local-density approximation (LDA), one of the most successful approximations in DFT. In thi...

arxiv.org/abs/2502.02378 #compchem

Time-reversal symmetry in RDMFT and pCCD with complex-valued orbitals Reduced density matrix functional theory (RDMFT) and coupled cluster theory restricted to paired double excitations (pCCD) are emerging as efficient methodologi

Finally published: Time-reversal symmetry in RDMFT and pCCD with complex-valued orbitals J. Chem. Phys., 162, 054716 (2025) doi.org/10.1063/5.0242504

Oh my! Thank you! 😊