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vmfreixas/README.md

Victor M. Freixas

Computational scientist · Excited-state dynamics · Ultrafast spectroscopy · Scientific machine learning

I build scalable methods and scientific software for understanding how molecules respond to light—from electronic-structure calculations and nonadiabatic dynamics to time-resolved spectroscopy and machine-learned Hamiltonians.

My work combines physical chemistry, high-performance computing, and reproducible software development. I have authored more than 40 peer-reviewed publications and contributed methods and tools for NEXMD- and NWChem-based research workflows.

Google Scholar · LinkedIn · Email

Current focus

  • Machine-learned quasi-diabatic Hamiltonians for excited-state molecular dynamics
  • Nonadiabatic dynamics and X-ray, UV–visible, and photoelectron spectroscopies
  • Molecular chirality analysis and real-space visualization
  • Scalable, reproducible workflows for quantum chemistry and molecular simulation

Selected projects

  • NQDH beating demo — A pre-trained neural quasi-diabatic Hamiltonian drives Libra/Ehrenfest dynamics for a 122-atom chromophore heterodimer and reproduces its S1/S2 vibronic quantum beating across a 300-trajectory ensemble.
  • tr-XPES — Python and MATLAB tools for calculating time-resolved X-ray photoelectron spectroscopy signals from NWChem electronic-structure calculations, accompanying the JCTC method paper.
  • Plotting chiral response — Tools to compute and visualize chiral population orbitals, accompanying the 2025 Chemical Science method paper on real-space visualization of X-ray circular dichroism.
  • Euler–Lagrange Solutions — A tested Python package that derives equations of motion symbolically with SymPy and integrates them numerically with SciPy.
  • STO–Gaussian overlaps — Orbital-overlap, density-matrix, and transition-density analysis connecting Slater- and Gaussian-type orbital representations.
  • Libra tutorials — Tutorials for quantum-classical dynamics, including nonadiabatic dynamics driven by a machine-learned Hamiltonian.

Research and impact

  • Developed excited-state simulation algorithms for systems with more than 200 atoms, with applications to dendrimers and organic photovoltaics.
  • Built and scaled molecular-dynamics and quantum-mechanical workflows on national high-performance-computing facilities.
  • Collaborated across physics, chemistry, computation, and experiment to turn new methods into reproducible research software.

Technical toolkit

  • Languages: Python, Fortran, MATLAB
  • Scientific computing: NumPy, SciPy, SymPy, Jupyter
  • Scientific ML: PyTorch, hippynn, learned molecular Hamiltonians
  • Electronic structure and dynamics: NWChem, PySCF, NEXMD, Libra, GROMACS
  • HPC and software: MPI, OpenMP, Slurm, Linux, Git, continuous integration

Let's connect

I am open to research collaborations and opportunities in computational chemistry, scientific machine learning, and scientific software engineering. The best way to reach me is by email or LinkedIn.

Popular repositories Loading

  1. tr-XPES tr-XPES Public

    This package calculates time-resolved X-ray Photoelectron Spectroscopy (tr-XPES) signals.

    Jupyter Notebook 1

  2. Plotting_chiral_response Plotting_chiral_response Public

    This package prepares chiral response contributions to be plotted as molden files

    Jupyter Notebook 1

  3. Euler_Lagrange_Solutions Euler_Lagrange_Solutions Public

    Auto-derive Euler–Lagrange equations from a Lagrangian; integrate and visualize in Jupyter.

    Python 1

  4. vmfreixas vmfreixas Public

    1

  5. STO_Gaussian_overlaps STO_Gaussian_overlaps Public

    This package calculates the overlaps between Slater Type Orbitals and Gaussian Type Orbitals, in particular STO-3G.

    Jupyter Notebook 1

  6. nqdh-beating-demo nqdh-beating-demo Public

    A frozen neural quasi-diabatic Hamiltonian drives Libra Ehrenfest dynamics and reproduces the S1/S2 vibronic beat (CyberTraining 2026)

    Python