:tocdepth: 1

.. _first-principles-calculations:

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First-principles calculations
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Phonons in δ-AlOOH
------------------

Raman and infrared spectra of δ-AlOOH show anomalies from hydrogen-bond disorder at much lower pressures than static harmonic theory predicts. Deep-potential molecular dynamics and phonon quasiparticle analysis at 300 K explain them as finite-temperature dynamics of the disordering hydrogen bonds.

- My contribution: the **harmonic SCAN-DFT phonon benchmark** that validates the deep potential and supplies the phonon eigenvectors
- Automated across pressures as a **Snakemake** workflow running **VASP** and **Phonopy** (SCAN, PAW, 520 eV, 2×2×4 supercells)
- Paper: `arXiv:2606.14590 <https://arxiv.org/abs/2606.14590>`__

.. figure:: ../img/research/alooh-phonons.png
   :width: 70%
   :align: center
   :alt: Harmonic phonon dispersion and vibrational density of states of delta-AlOOH from SCAN-DFT and SCAN-DP

   **Harmonic phonon dispersion and vibrational density of states (VDoS)** for δ-AlOOH from SCAN-DFT and SCAN-DP at (a) 0 GPa and (b) 90 GPa.

Monte Carlo geometry optimization of clusters
---------------------------------------------

As an undergraduate at The Cooper Union with Prof. Robert Q. Topper, I worked on finding the lowest-energy structures of atomic and molecular clusters with simulated annealing Monte Carlo.

- **TransRot** optimizes cluster geometries through purely translational and rotational moves
- **Mag-walking** helps molecules reorient and escape high-energy local minima; **sawtooth annealing** samples both molten and crystalline structures
- Code: `TransRot <https://github.com/RQTopper/TransRot>`__ · Paper: `ACS Symposium Series <https://doi.org/10.1021/bk-2022-1428.ch002>`__

Co-authored publications
------------------------

- **Lattice dynamics and the spectroscopic signatures of H-bond disorder in δ-AlOOH.** C. Luo, S. Lee, H. Wang, Z. Zhang, R. Wentzcovitch, `arXiv:2606.14590 <https://arxiv.org/abs/2606.14590>`__ (2026).
- **TransRot: a portable software package for simulated annealing Monte Carlo geometry optimization of atomic and molecular clusters.** R. Q. Topper, S. L. Topper, S. Lee, `ACS Symposium Series <https://doi.org/10.1021/bk-2022-1428.ch002>`__ 1428 (2022).