Projects

At Zapata Computing

Lots of fun and interesting stuff on which I won't give details, see Zapata's website for the most up-to-date information.

In the Head-Gordon group (UC Berkeley)

Compressed representation of dispersion

I examined the nature of dispersion interactions by analyzing the CCSD T2 amplitudes in a local basis. Singular Value Decomposition of these amplitudes yields a very compact representation, from which I extract virtual orbitals specifically tailored for dispersion. These orbitals are connected to the multipole expansion of dispersion and represent dipolar-dipolar, dipolar-quadrupolar and quadrupolar-quadrupolar correlations. This work is related to the PNO technique and opens up new ways to efficiently represent dispersion. (10.1063/1.4997186)

The analyses tools were implemented as object-oriented C++ code in the commercial electronic structure software Q-Chem.

Quantum computing

In a collaboration with Ivano Tavernelli, technical leader of theoretical quantum computing at IBM Research, Zurich. Optimization of Unitary Coupled-Cluster for Variational Quantum Eigensolver, submitted for publication.

Supervision of Master thesis

I designed and supervised the research project on which Pauline Ollitrault worked for 6 months before obtaining her Master thesis. Pauline is currenly a PhD candidate at IBM Research laboratories in Zurich, Switzerland.

Implementation of a new feature in Q-Chem

More to come after publication, collaborative project with Head-Gordon group members and Q-Chem employees to write several thousand lines of C++ code.

In the Sherrill group (GeorgiaTech)

Collaboration on Photosystem II spectroscopy

IR spectroscopic data from Prof. Bridgette Barry and Udita Brahmachari, supported by simulated IR spectra that I computed, indicate that a protonated water cluster near a chloride ion is involved in an internal proton transfer step in the S1 to S2 transition of the oxygen evolving complex in Photosystem II (10.1021/acs.jpcb.7b08358 and 10.1021/acs.jpcb.9b01523).

Implementation of Open-shell Symmetry-Adapted Perturbation Theory (SAPT)

I generalized the very efficient closed-shell SAPT code to open-shell cases in the software Psi4 and performed the then largest open-shell SAPT computation to date, examining the change in pi-stacking interactions of a base pair ladder upon oxidation (10.1063/1.4963385). To facilitate these computations, I also improved considerably the efficiency of the UHF stability analysis in Psi4.

Optimization of Fock builder implementation

I rewrote the disk-based Fock builder in Psi4 to minimize disk access and use batching of integral computation over multiple threads (OpenMP). Each thread now computes integrals in specialized buffers, and one separate thread is performing asynchronous write operations in the appropriate file as results become available. I also added a fully in-code algorithm when enough memory is available. The various algorithms all derive from the same base class for convenience.

Complete derivation of open-shell SAPT

To make sure the implementation of open-shell SAPT was correct, since unfortunately most published formulae have typos, I re-derived all terms in open-shell SAPT0 from scratch. The full document is available as a pdf.

Intramolecular SAPT

In collaboration with Rob Parrish, we published a mathematically simple version of intramolecular SAPT that is based on HF-in-HF embedding. All terms in SAPT0 are available in the intramolecular version since only the zeroth-order wavefunction is different from the intermolecular case (10.1063/1.4927575).

In the Corminboeuf group (EPFL)

Intramolecular Symmetry-Adapted Perturbation Theory

My early work on intramolecular SAPT was devoted to designing a reliable zeroth-order wavefunction that would exclude the non-covalent interactions of interest while still describing all other interactions in a molecule. I implemented in Fortran 90 an approach based on the Chemical Hamiltonian (10.1063/1.4871116) which was later used to derive the necessary SAPT0 energy terms (10.1063/1.4936830).

Chemical concepts

I participated in the writing of a review summarizing the quantification of a number of chemical concepts. Often, several different methods are available for quantification, for example to compute bond orders and partial charges. We discussed the pros and cons of the most common methods (10.1039/C2CS35037H).

I also designed an index to characterize the propensity of a planar molecule for pi-stacking interactions based on the LOL isosurface for the electrons (10.1039/C2CC33886F).

Catalysis and reactivity

I collaborated with Dr. Matthew Wodrich and the Cramer experimental group on a Rh(III)-catalyzed dihydroisoquinolone synthesis. Specifically, I wrote and solved the system of differential equations describing the entire kinetic network of the computed catalytic cycle (10.1002/chem.201404515).

I worked in direct collaboration with Dr. Astrid J. Olaya and the Girault group on the metal-free four-electron reduction of dioxygen catalyzed by tetrathiafulvalene (TTF). My computations revealed that a TTF quadruplex likely played the role of the catalyst in this reaction (10.1021/ja203251u).

Thermochemistry

I modeled the enthalpy of formation of regular, methylated and permethylated linear alkanes by a simple increment system. Branched alkanes are generally known to be more stable than their linear counterparts, however this is not true beyond some degree of branching where steric repulsions start to dominate the interactions (10.1021/ol1010642).

I collaborated with Dr. Matthew Wodrich to investigate the strain in carbomeric cycloalkanes (10.1021/jp1029322) and the thermochemistry of hydrocarbon radicals (10.1021/jp3061653).