Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V20: Heat Transport in Condensed Systems IIIFocus Live
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Sponsoring Units: DCOMP Chair: Vasili Perebeinos, State Univ of NY - Buffalo |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V20.00001: Lattice Thermal Conductivity in Binary Rocksalt and Zincblende Compounds Including Higher-Order Anharmonicity Yi Xia, Vinay Ishwar Hegde, Koushik Pal, Xia Hua, Dale Gaines II, Shane Patel, Jiangang He, Muratahan Aykol, Christopher Wolverton Heat conduction plays a critical role in the performance of microelectronic and energy-conversion devices. To meet the cooling demands of microprocessors and the efficiency of energy convertors, researchers are particularly interested in identifying semiconducting materials with extreme thermal conductivities. Surprisingly, these have been discovered in binary cubic compounds. A comprehensive understanding of their underlying heat transfer mechanism is therefore of fundamental importance. Here, we compute the thermal transport properties of 37 binary rocksalt and zincblende compounds and study how their thermal transport properties are affected by quartic anharmonicity. We find that including quartic anharmonicity always decreases the lattice thermal conductivity in zincblendes but can either increase or decrease the conductivity in rocksalts. Among notable examples, we show that four-phonon scattering is unprecedentedly strong in the zincblende mercury telluride, and strong phonon scattering leads to a possible breakdown of the phonon gas model in the rocksalt silver chloride. Our results pave the way for an in-depth understanding of heat transfer in a broad class of technologically important compounds, which may guide future engineering. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V20.00002: Green-Kubo Thermal Conductivities with Message-Passing Neural Networks Marcel Langer, Florian Knoop, Christian Carbogno, Matthias Scheffler, Matthias Rupp Accurate, precise, and efficient computational access to thermal conductivities of known and novel materials is a challenging and urgent problem that concerns scientific understanding as well as industrial applications. The Green-Kubo (GK) method combined with first-principles calculations enables the accurate determination of thermal conductivities, even for strongly anharmonic materials [1], but its applicability is limited by the high computational cost of the long dynamics simulations required. Machine-learning potentials can reduce this cost by orders of magnitude. Message-passing neural networks (MPNNs) acting on a graph representation of a material are promising for this application due to their relational inductive bias and implicit long-range nature. They model interactions between atoms as multiple iterations of a short-range interaction, allowing information to propagate beyond local environments while avoiding the costly evaluation of explicit long-range interactions. We show how the GK method can be formulated and implemented using MPNNs, and benchmark their performance for zirconium dioxide, a strongly anharmonic material. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V20.00003: Relaxation pathways for vibrational modes in molecular crystal α-RDX Gaurav Kumar, Peter W. Chung Understanding of phonon properties in molecular crystals is critical due to their influence over, for instance, the sensitivity of explosives. In particular, phonons are believed to play a key role in the transfer of energy between the vibrational modes which may result in phenomena leading to initiation. In this work, we investigate the mechanisms for relaxation of the modes in the Van der Waals bonded molecular crystal α-RDX, using the ALD formalism for three phonon scattering. We examine pathways for the transfer of energy from the low frequency lattice vibrations to the high frequency intramolecular vibrational modes which result in large bond distortions and concentration of energy in some modes which may lead to initiation. We investigate the contribution of all phonon modes to bond distortions and identify key inter and intra-molecular interactions responsible for the transfer of energy and relaxation of the modes. Our preliminary results indicate that ALD based technique slightly overpredicts the thermal conductivity since only up to third order phonon scattering processes are considered. We also observe that the low frequency modes (< 4 THz) contribute ~90% to the total bond strain, among which N-N and N-O bonds were found to exhibit the largest strains and rotations. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V20.00004: Unravelling the self doping induced lowering in the lattice thermal conductivity of n-type thermoelectric half Heusler compounds Parul Raghuvanshi, Dipanwita Bhattacharjee, Amrita Bhattacharya Ternary intermetallic half Heusler (HH) compounds (XYZ) with 18 valence electron count viz. ZrNiSn, ZrPdSn, and ZrCoSb, have revealed interesting thermoelectric properties pertaining to their narrow bandgap and flexibility in undergoing doping. Exemplarily, it has been experimentally observed that a slight change in the content of Y-site atoms (by ~3% i.e. n =0.03 in ZrY1+nZ) leads to drastic lowering in the lattice thermal conductivity (kL) by more than ~ 60 % in all these compounds [1]. Thus, it is interesting to explore the impact of these off stoichiometric defects on the transport coefficients and the underlying physical mechanisms. We have performed the anharmonic lattice dynamics calculations using the Boltzmann transport equation under the framework of density functional theory to analyze the ongoing phenomena. It reveals that the excess atoms present at the vacant sites as interstitial defects act as phonon scattering center and enable strong scattering of the thermal phonons, resulting in a significant reduction of the kL. Furthermore, the excess electrons beyond 18 provide substantial doping (n-type) which improves the electronic transport coefficients. Our findings can be extended to other HH compounds. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V20.00005: Disentangling mass effects from crystal chemistry in the thermal properties of III-V insulators Sabrina Li, Ethan Ritz, Nicole Benedek BAs, a III-V insulator, has a thermal conductivity comparable to diamond and a higher thermal conductivity than other cubic III-V boron compounds. The origin of this high thermal conductivity has been attributed to the mass ratio and unique chemical bonding character of BAs, both of which give rise to specific features in the phonon dispersion curve that determine the available scattering phase space [Phys. Rev. X 10 021063 (2020)]. We use first-principles density functional theory in combination with the Boltzmann transport equation to systematically explore and disentangle the effects of mass ratio and bonding and chemistry on the thermal conductivity of the entire column of cubic III-V boron compounds, from c-BN to BSb. Our preliminary results and previous work [J. Appl. Phys. 116 073503 (2014)] suggest that although the mass ratio of BAs may optimally maximize thermal conductivity, there may be a pathway to further increasing thermal conductivity through modifying bonding and chemistry. Our work provides hints regarding the chemical characteristics of high thermal conductivity materials. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V20.00006: Interplay of interfacial scattering and internal phonon scattering for thermal transport across a Si/Ge interface Xun Li, Sangyeop Lee Interfacial resistance between solids has drawn significant interest due to its importance in applications including thermal management in electronic devices. The widely used Landauer formula fails in describing interfacial resistance because it neglects internal phonon scattering. A modified Landauer formula which includes this important contribution, assumes phonons follow the bulk distribution, neglecting the non-equilibrium distribution. Here, we present our examination of interfacial phonon transport by solving the Peierls-Boltzmann equation in both real and reciprocal spaces with inputs from first-principles. The results show that there is a strongly non-equilibrium distribution near the interface due to the complex interplay between the interface scattering and internal phonon scattering. This non-equilibrium distribution decays with distance from the interface and eventually recovers to the bulk phonon distribution. We find that the internal phonon scattering near the interface provides an important contribution to the overall interfacial resistance. Our study provides insights into large discrepancies between experimentally measured interfacial resistances and those calculated from the Landauer formula, thus providing a useful way to interpret experimental data. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V20.00007: A hybrid model for thermal transport in Si nanostructures from first principles Aliya Qureshi, Zlatan Aksamija Phonon scattering plays an i mportant role in limiting thermal conductivity. Analytical expressions used in the Callaway model to calculate normal (N) and umklapp (U) scattering serve as a valuable tool to study heat transfer. However, calculations using these empirical scattering rates lack predictive power and transferability for a range of temperature (T) relative to the more computationally expensive iterative numerical approach. We present a hybrid approach where we calculate N and U rates from the first principles and implement them in the Callaway model for the calculation of thermal conductivity in silicon (Si) over a wide T range of 10K to 425K. In addition, the model accurately captures momentum-dependent boundary roughness scattering, which is particularly important in nanostructures. Conductivities calculated using our hybrid approach are in good agreement with measured values of natural and isotopically pure Si over the entire range of T without any adjustable parameters. A central feature of this approach is that it captures the interaction between internal and boundary conditions more accurately than some iterative approaches while being much more computationally efficient. The approach we presented can be used in future thermal transport studies of nanostructures. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V20.00008: Thermal transport from first principles beyond phonons Florian Knoop, Thomas Alexander Reichmanis Purcell, Matthias Scheffler, Christian Carbogno We present a systematic and numerically precise first-principles search for thermal insulators in material space. Using the high-throughput framework FHI-vibes [1] and a recently developed measure for the strength of anharmonicity [2], we first screen over thousands of materials, including complex oxides, chalcogenides, and ternary perovskites, to single out dozens of strongly anharmonic systems with potential for ultra-low thermal conductivity κ. We then perform ab initio Green-Kubo simulations on these candidates to accurately determine κ [3], thereby naturally including anharmonic effects and dynamical processes that cannot be described in a phonon picture, e.g., short-lived metastable configurations and structural phase transitions. We quantify and discuss the importance of such strong anharmonic effects on thermal transport across material space, and highlight systems for which perturbative approaches break down. |
Thursday, March 18, 2021 4:36PM - 5:12PM Live |
V20.00009: Thermal Conductivity of CaSiO3 Perovskite at Lower Mantle Conditions Invited Speaker: Zhen Zhang Thermal conductivity (κ) of mantle minerals modulates strongly both the style of mantle convection and the time scale of the Earth’s mantle and core cooling. It is therefore a fundamental parameter for geodynamic modeling. Cubic CaSiO3 perovskite (cCaPv) is believed to be the third most abundant mineral in the lower mantle (LM) (7 vol%). However, despite its importance, investigations of its properties are challenging because of its strong anharmonicity. cCaPv is dynamically unstable at low temperatures and its phonon spectrum has imaginary frequencies from harmonic phonon calculation. Particularly for κ, prevailing theoretical approaches such as perturbative methods encounter difficulties in dealing with such strong anharmonicity. Experimental measurements at relevant high pressures and temperatures are equally challenging. Therefore, no previous estimate of cCaPv’s κ exists at mantle conditions, experimental or theoretical. Here we present ab initio quantum mechanical results of this property obtained using an established phonon quasiparticle approach that can address the strongly anharmonic situation in cCaPv. These results are substantiated by direct experimental measurements of this property at LM conditions. These results and data agree very well and reveal a surprisingly large κ of cCaPv compared to MgSiO3-perovskite, which is only weakly anharmonic. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V20.00010: On the possible explanation of the reduced thermal conductivity in molecular forests Debashish Mukherji, Aashish Bhardwaj, Srikantha Phani, Alireza Nojeh The heat propagation in quasi-one dimensional materials (Q1DMs) often appears paradoxical. For example, an isolated Q1DM, such as a nanowire, carbon nanotube, or polymer, can exhibit a high thermal conductivity κ, assemblies of the same materials show a reduction in κ. Here, the complex structures of these assemblies have hindered the emergence of a clear molecular picture of this intriguing phenomenon. We combine multiscale simulation with the concepts known from polymer physics and thermal transport to unveil a generic picture of κ reduction in molecular forests. We show that a delicate balance between the segment orientations, the persistence length of the Q1DM and the flexural vibrations govern the behavior of κ. |
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