Charge state and entropic effects affecting the formation and dynamics of divacancies in 3C-SiC
Not Available
Zhang, Cunzhi↗
Engineering topics
Zhang, Cunzhi
Publications and source records attributed to Zhang, Cunzhi.
Engineering the formation of spin-defects from first principles
The full realization of spin qubits for quantum technologies relies on the ability to control and design the formation processes of spin defects in semiconductors and insulators. We present a computational protocol to investigate the synthesis of point-defects at the atomistic level, and we apply it to the study of a promising spin-qubit in silicon carbide, the divacancy (VV). Our strategy combines electronic structure calculations based on density functional theory and enhanced sampling techniques coupled with first principles molecular dynamics. We predict the optimal annealing temperatures for the formation of VVs at high temperature and show how to engineer the Fermi level of the material to optimize the defect’s yield for several polytypes of silicon carbide. Our results are in excellent agreement with available experimental data and provide novel atomistic insights into point defect formation and annihilation processes as a function of temperature.
36 MATERIALS SCIENCE↗
Extremely Large Response of Phonon Coherence in Twisted Penta‐NiN 2 Bilayer
Abstract Twisting has recently been demonstrated as an effective strategy for tuning the interactions between particles or quasi‐particles in layered materials. Motivated by the recent experimental synthesis of pentagonal NiN 2 sheet [ACS Nano2021, 15, 13539], for the first time, the response of phonon coherence to twisting in bilayer penta‐NiN 2 , going beyond the particle‐like phonon transport is studied. By using the unified theory of phonon transport and high order lattice anharmonicity, together with the self‐consistent phonon theory, it is found that the lattice thermal conductivity is reduced by 80.6% from 33.35 to 6.47 W m −1 K −1 at 300 K when the layers are twisted. In particular, the contribution of phonon coherence is increased sharply by an order of magnitude, from 0.21 to 2.40 W m −1 K −1 , due to the reduced differences between the phonon frequencies and enhanced anharmonicity after the introduction of twist. The work provides a fundamental understanding of the phonon interaction in twisted pentagonal sheets.
Chemistry↗
Thermal Conductivity of Water at Extreme Conditions
Not Available
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Photoelectron spectra of water and simple aqueous solutions at extreme conditions
We present calculations of the photoelectron spectra of water and a simple solution of NaCl under pressure at conditions relevant to the Earth’s interior (11 GPa and 1000 K).
Ye, Zifan↗
Nonperturbative phonon scatterings and the two-channel thermal transport in Tl 3 VSe 4
We review the role of nonperturbative phonon scattering in strongly anharmonic materials having ultralow lattice thermal conductivity with unusual temperature dependence. We take Tl 3 VSe 4 as an example and investigate its lattice dynamics using perturbation theory (PT) up to the fourth order and molecular dynamics (MD) with a machine-learning potential. We find distinct differences of phonon linewidth between PT and MD in the whole Brillouin zone. The comparison between the theoretical phonon linewidths and experiments suggests that PT severely underestimates the phonon scatterings, even when the fourth-order anharmonicity is included. Moreover, we extend our calculations to higher temperatures and evaluate the two-channel thermal conductivity based on the unified theory developed by Simoncelli et al. [Nat. Phys. 15, 809 (2019)]. We find a crucial coherence contribution to the total thermal conductivity at high temperatures. Our results pave the path for future studies of phonon properties and lattice thermal conductivities of strongly anharmonic crystals beyond the conventional PT realm.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Dissociation of salts in water under pressure
The investigation of salts in water at extreme conditions is crucial to understanding the properties of aqueous fluids in the Earth. We report first principles (FP) and classical molecular dynamics simulations of NaCl in the dilute limit, at temperatures and pressures relevant to the Earth's upper mantle. Similar to ambient conditions, we observe two metastable states of the salt: the contact (CIP) and the solvent-shared ion-pair (SIP), which are entropically and enthalpically favored, respectively. We find that the free energy barrier between the CIP and SIP minima increases at extreme conditions, and that the stability of the CIP is enhanced in FP simulations, consistent with the decrease of the dielectric constant of water. The minimum free energy path between the CIP and SIP becomes smoother at high pressure, and the relative stability of the two configurations is affected by water self-dissociation, which can only be described properly by FP simulations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗