Excited-state from solving the Bethe-Salpeter equation and spin dynamics from the density-matrix formalism

Optoelectronic and spin-optotronic properties of low dimentional materials including many body interactions

Low dimensional materials including (quantum dots, nanowires/nanotubes, 2D materials) have highly tunable optical properties and stronger electron hole interactions comparing with 3D materials. We solve Bethe-Salpeter Equations (BSE) without explicit empty electronic states to treat e-h interactions explicitly[1-3] and optimize their optical properties by forming interfaces, introducing defects and surface functionalization. We study spin-defects in 2D materials for quantum information applications[4,8], focusing on their excited state lifetime and spin relaxation/decoherence mechanism. 

We develop charge correction methods that can provide reliable charged defect properties for 2D systems and  general interfaces[4]. We develop methodology to compute exciton radiative[5] and nonradiative recombination rates[6], as well as intersystem-crossing rate[7] including electron-hole and electron-phonon couplings. More recently, we developed ab-initio spin dynamics from density-matrix formalism, including quantum descriptions of electron-phonon, electron-electron, electron-defect scattering, and spin-orbit couplings[7,10,11]. This framework can predict spin relaxation and decoherence time accurately from first-principles and determine the dominant decoherence mechanism for general solid-state systems. 

Representative papers:

11. “Ab initio Ultrafast Spin Dynamics in Solids”, J. Xu, A. Habib, R. Sundararamanand Y. Ping*, Physical Review B, 104, 184418, (2021). Editor’s Suggestions. Physics Magazine

10. “Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics”, J. Xu, H. Takenaka, A. Habib, R. Sundararaman*, Y. Ping*, Nano Letters, 21, 9594, (2021).

9.”Substrate Screening Approach for Quasi-particle Energies of Two-dimensional Interfaces with Lattice Mismatch, Chunhao Guo, Junqing Xu, Dario Rocca, Yuan Ping*, Physical Review B, 102, 205113, (2020), Editors’ Suggestionarxiv.2007.07982 

8. “Intersystem Crossing and Exciton-Defect Coupling of Spin Defects in Hexagonal Boron Nitride”, T. Smart, K. Li, J. Xu, Y. Ping*, npj Computational Materials, 7, 59, (2021).

7. “Spin-phonon Relaxation from a Universal Ab initio Density-matrix Approach, Junqing Xu, Adela Habib,  Sushant Kumar,  Feng Wu, Ravishankar Sundararaman* , and Yuan Ping*, Nature Communications, 11, 2780, (2020). arXiv: 1910.14198   UCSC News Press,  Santa Cruz Tech Beat,  ScienceDaily, Phys.Org,  SwissQuantumHub

6. “Carrier Recombination Mechanism at Defects in Wide Band gap Two-dimensional Materials from First principles”, Feng Wu, Tyler J. Smart, Junqing Xu and Yuan Ping*, Physical Review B (Rapid Communications), 100, 081407(R), (2019). arXiv:1906.02354

5. “Dimensionality and Anisotropicity Dependence of Radiative Recombination in Nanostructured Phosphorene”, Feng Wu, Dario Rocca, and Yuan Ping*, Journal of Materials Chemistry C, (Emerging Investigators themed issue), 7, 12891, (2019). Cover Art.  Preprint: arXiv:1903.11773

4.First-principles Engineering of Charged Defects for Two-dimensional Quantum Technologies”,F. Wu, A. Galatas, R. Sundararaman, D. Rocca and Y. Ping, Physical Review Materials (Rapid Communication), 1, 071001(R) (2017),

3. “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, Chemical Society Reviews, 42, 2437, (2013).

2. “Ab-initio Calculations of Absorption Spectra of Semiconducting Nanowires within Many Body Perturbation Theory”, Y. Ping, D. Rocca, D. Lu and G. Galli, Physical Review B, 85, 035316, (2012).

1. “Bethe-Salpeter Equation Without Empty Electronic States: Application to Bulk Systems”, D. Rocca, Y. Ping, G. Galli, Physical Review B, 85, 045116, (2012).

Improving optical and carrier transport properties by atomic doping

Polarons and excitons in transition metal oxides

Defects and doping can significantly modify the electronic structure, optical and carrier transport properties of transition metal oxides (TMOs). We coupled the Landau-Zener theory generalized to non-adiabatic electron transfer with kinetic Monte Carlo samplings to compute small polaron hopping mobility in doped TMOs, reveal  the fundamental mechanism that how dopants can improve polaronic conduction in TMOs. We also compute spectroscopic signatures of polaron and exciton states in TMOs. 

Representative Papers:

Optical Absorption Induced by Small Polaron Formation in Transition Metal Oxides – The Case of Co3O4”, Tyler J. Smart, Tuan Anh Pham, Yuan Ping*, and Tadashi Ogitsu*, Physical Review Materials (Rapid Communications), 3, 102401(R) (2019). arXiv:1909.08653

Combining Landau-Zener Theory and Kinetic Monte Carlo Sampling for Small Polaron Mobility of Doped BiVO4 from First-principles”, Feng Wu and Yuan Ping, Journal of Materials Chemistry A,  6, 20025-20036 (2018).  arXiv:1808.02507

Mechanistic Insights of Enhanced Spin Polaron Conduction in CuO through Atomic Doping”, Tyler Smart, Allison Cardiel, Feng Wu, Kyoung-Shin Choi and Yuan Ping, npj Computational Materials4, 61 (2018).

“Simultaneous Enhancements in Photon Absorption and Charge Transport of BiVO4 Photoanodes for Solar Water Splitting”, T. Kim, Y. Ping, G. Galli and K. Choi, Nature Communications, 6, 8769, (2015). (Highlighted in News of University of Chicago)

“Thermally Stable N2-intercalated WO3 Photoanodes for Water Oxidation, Q. Mi, Y. Ping, Y. Li, B. Brunschwig, G. Galli, H. Gray and N. Lewis, Journal of the American Chemical Society, 134, 18318, (2012). (Highlighted in the feature article of CCI Solar)

“Synthesis, Photoelectrochemical Properties, and First Principle Study of n-type CuW1-xMoxO4 Electrodes Showing Enhanced Visible Light Absorption”, J. Hill, Y. Ping, G. Galli, K. Choi, Energy & Environmental Science (Communication), 6, 2440, (2013).

Using DFT and GW approximations for the band alignment, charge transfer and catalytic properties

Charge transfer and catalytic properties at complex solid-liquid interfaces

Charge transfer and catalytic reactions at solid-liquid interfaces are important for solar-to-fuel, fuel cell and battery applications. We use DFT and GW approximations for the band alignment and charge transfer at the solid-liquid interfaces with implicit or explicit solvents; furthermore, we study surface catalytic reaction mechanisms including thermodynamic reaction free energies, kinetic barriers and reaction rates at the constant potential condition, directly comparing with experimental electrochemical Tafel plots and overpotential measurements.

Representative papers:

Ruthenium atomically dispersed in carbon outperforms platinum toward hydrogen evolution in alkaline media”, Bingzhang Lu, Lin Guo, Feng Wu, Yi Peng, Jia En Lu, Tyler J. Smart, Nan Wang, Y. Zou Finfrock, David Morris, Peng Zhang, Ning Li, Peng Gao, Yuan Ping*, and Shaowei Chen*, Nature Communications, 10, 631 (2019).

Theoretical and Experimental Insight into the Effect of Nitrogen Doping on Hydrogen Evolution Activity of Ni3S2 in Alkaline Medium”, T. Kou, T. Smart, B. Yao, I. Chen, D. Thota, Y. Ping*, Y. Li*,  Advanced Energy Materials, 8, 1703538 (2018).

Modeling Heterogeneous Interfaces for Solar Water Splitting, T. Pham, Y. Ping and G.Galli, Nature Materials, 16, 401–408 (2017) 

“The Reaction Mechnism with Free Energy Barriers at Constant Potentials for the Oxygen Evolution Reaction at IrO2(110) Surface”, Y. Ping, R. Nielsen, W. Goddard III, Journal of the American Chemical Society139, 149-155, (2017).

“Energetics and Solvation Effects at the Photoanode/Catalyst Interface:Ohmic Contact versus Schottky Barrier”, Y. Ping, W. Goddard III and G.Galli, Journal of the American Chemical Society, 137, 5264, (2015).

“Solvation Effect on Band Edge Positions of Photocatalysts from First Principles”, Y. Ping, R. Sundararaman, and W. Goddard III, Physical Chemistry Chemical Physics, 17, 30499, (2015). (Highlighted in the feature article of Joint Center for Artificial Photosynthesis)