Electronic Spectroscopy

Photoluminescence and absorption spectra

We developed ab initio approaches to compute vibrationally resolved optical spectra of large systems, with focus on point defects in semiconductors. We implemented the calculation of excited state analytical nuclear forces for both spin-conserving and spin-flip time-dependent density functional theory (TDDFT) in the WEST code, thus enabling the study of excited state potential energy surfaces. We use the Huang-Rhys theory to describe the coupling between the vibrational and the electronic degrees of freedom in the optical processes, and the generating function approach to compute vibrationally resolved spectra. We investigated the vibrationally resolved photoluminescence, absorption, and photo-ionization spectra of spin-defects in semiconductors, e.g. the nitrogen-vacancy center in diamond and divacancy centers in silicon carbide.

• "Quantum Vibronic Effects on the Excitation Energies of the Nitrogen-vacancy Center in Diamond", A. Kundu and G. Galli, J. Phys. Chem. Lett. 15, 802-810 (2024).
• "Excited state properties of point defects in semiconductors and insulators investigated with time-dependent density functional theory", Y. Jin, V. W.-z. Yu, M. Govoni, A. C. Xu, and G. Galli, J. Chem. Theory Comput. 19, 8689–8705 (2023).
• "Vibrationally resolved optical excitations of the nitrogen-vacancy center in diamond", Y. Jin, M. Govoni, and G. Galli, npj Comput. Mater. 8, 238 (2022).
• "Five-second coherence of a single spin with single-shot readout in silicon carbide", C. P. Anderson, E. O. Glen, C. Zeledon, A. Bourassa, Y. Jin, Y. Zhu, C. Vorwerk, A. L. Crook, H. Abe, J. Ul-Hassan, T. Ohshima, N. T. Son, G. Galli, and D. D. Awschalom, Sci. Adv. 8, eabm5912 (2022).
• "Photoluminescence spectra of point defects in semiconductors: Validation of first-principles calculations", Y. Jin, M. Govoni, G. Wolfowicz, S. E. Sullivan, F. J. Heremans, D. D. Awschalom, and G. Galli, Phys. Rev. Mater. 5, 084603 (2021).

Quantum Vibronic Effects on the Electronic Properties of Solids and Molecules

We have been exploring several approaches to investigate vibronic effects on the electronic properties of solids and molecules. One approach uses density functional or density matrix perturbation theory and efficiently combines the computation of electron–electron and electron–phonon self-energies. Another approach combines path integral first principles molecular dynamics (FPMD) with a colored noise thermostat. We have used these methods to study molecular crystals, several carbon systems, including amorphous carbon, diamond and point defects in diamond, and water and ice..

• "Nuclear Quantum Effects on the Electronic Structure of Water and Ice", Margaret Berrens, Arpan Kundu, Marcos F. Calegari Andrade, Tuan Anh Pham, Giulia Galli, and Davide Donadio, J. Phys. Chem. Lett. 15, 6818–6825 (2024).
• "Quantum Vibronic Effects on the Excitation Energies of the Nitrogen-vacancy Center in Diamond", Arpan Kundu and Giulia Galli, J. Phys. Chem. Lett. 15, 802-810 (2024).
• "Quantum Vibronic Effects on the Electronic Properties of Molecular Crystals", Arpan Kundu and Giulia Galli, J. Chem. Theory Comput. 19, 4011–4022 (2023).
• "Quantum simulations of thermally activated delayed fluorescence in an all-organic emitter", Tommaso Francese, Arpan Kundu, Francois Gygi, and Giulia Galli, Phys. Chem. Chem. Phys. 24, 10101 (2022).
• "Influence of nuclear quantum effects on the electronic properties of amorphous carbon", A. Kundu, Y. Song, and G. Galli, PNAS 119 (31), e2203083119 (2022).
• "Computational protocol to evaluate electron-phonon interactions within density matrix perturbation theory", H. Yang, M. Govoni, A. Kundu, and G. Galli, J. Chem. Theory Comput. 18, 6031 (2022).
• "Combined first-principles calculations of electron-electron and electron-phonon self-energies in condensed systems", H. Yang, M. Govoni, A. Kundu, and G. Galli, J. Chem. Theory Comput. 17, 7468 (2021).
• "Quantum Vibronic Effects on the Electronic Properties of Solid and Molecular Carbon", A. Kundu, M. Govoni, H. Yang, M. Ceriotti, F. Gygi, and G. Galli, Phys. Rev. Mat. 5, L070801 (2021).
• "Coupling First Principles Calculations of Electron-Electron and Electron-Phonon Scattering, and Applications to Carbon-based Nanostructures", R. L. McAvoy, M. Govoni, and G. Galli, J. Chem. Theory Comput., 14, 6269 (2018).

Data Collections

The WEST Data Collections provide open web-based access to electronic structure properties computed with WEST. Explore the GW100 and GW-SOC81 sets.

GW and BSE calculations

We have developed ab initio approaches to compute optical absorption and emission spectra of molecules and solids, which are suitable for the study of large systems and give access to spectra within a wide energy range. For absorption spectra, the quantum Liouville equation is solved iteratively within first order perturbation theory, with a Hamiltonian containing a static self-energy operator. For emission spectra, we use a spectral decomposition of the static dielectric matrix as a basis for the frequency dependent density-density response function. Explicit calculations of single particle excited states and inversion and storage of dielectric matrices are avoided using techniques based on Density Functional Perturbation Theory.

• "Machine Learning Dielectric Screening for the Simulation of Excited State Properties of Molecules and Materials", Sijia Dong, Marco Govoni and Giulia Galli, Chem. Sci. 12, 4970-4980 (2021)
• "Finite-field approach to solving the Bethe-Salpeter equation", Ngoc Linh Nguyen, He Ma, Marco Govoni, Francois Gygi and Giulia Galli, Phys. Rev. Lett. 122, 237402 (2019)
• "Implementation and Validation of Fully-Relativistic GW Calculations: Spin-Orbit Coupling in Molecules, Nanocrystals and Solids", P. Scherpelz, M. Govoni, I. Hamada, and G. Galli , J. Chem. Theory Comput. 12 (8), 3523-3544 (2016)
• "Large Scale GW calculations", M. Govoni and G. Galli, J. Chem. Theory Comput. 11, 2680 (2015)
• "Predictive Theory and Modelling of Heterogeneous Interfaces", Tuan Anh Pham, Ph.D. Thesis (2014)
• "GW calculations using the spectral decomposition of the dielectric matrix: Verification, validation, and comparison of methods", T.A. Pham, H.-V. Nguyen, D. Rocca and G. Galli, Phys. Rev. B 87, 155148 (2013)
• "Spectral representation analysis of dielectric screening in solids and molecules", A. Kaur, E.R. Ylvisaker, D. Lu, T.A. Pham, G. Galli and W.E. Pickett, Phys. Rev. B 87, 155144 (2013)
• "Electronic excitations in light absorbers for photoelectrochemical energy conversion: first principles calculations based on many body perturbation theory", Y. Ping, D. Rocca and G. Galli, Chem. Soc. Rev. 42, 2437 (2013)
• "A block variational procedure for the iterative diagonalization of non-Hermitian random-phase approximation matrices", D. Rocca, Z. Bai, R. Li and G. Galli, J. Chem. Phys. 136, 034111 (2012)
• "Solution of the Bethe-Salpeter equation without empty electronic states: application to the absorption spectra of bulk systems", D. Rocca, Y. Ping, R. Gebauer and G. Galli, Phys. Rev. B. 85, 045116 (2012)
• "Improving accuracy and efficiency of calculations of photoemission spectra within many body perturbation theory", H. Nguyen, T. Pham, D. Rocca and G. Galli, Phys. Rev. B. 85, 081101(R) (2012)
• "Ab initio calculations of optical absorption spectra: Solution of the Bethe-Salpeter equation within density matrix perturbation theory", D. Rocca, D. Lu, and G. Galli, J. Chem. Phys. 133, 164109 (2010)