Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R17: Matter in Extreme Environments: Theoretical Methods and Applications IIFocus

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Sponsoring Units: DCOMP Chair: Jorge Botana, California State University, Northridge Room: BCEC 156A 
Thursday, March 7, 2019 8:00AM  8:36AM 
R17.00001: New directions for random search Invited Speaker: Chris Pickard Genuinely new knowledge and scientific insight can be obtained about dense matter by combining random numbers with reliable and efficient first principles methods. Diverse ensembles of initial structures can be generated, and structurally optimized. The resulting low energy structures are candidates for stable, and metastable, phases and/or defects that might be experimentally realized. This, of course, depends on a sufficiently broad and thorough sampling of configuration space. 
Thursday, March 7, 2019 8:36AM  8:48AM 
R17.00002: Theoretical Prediction of Superhard Materials with the XtalOpt Evolutionary Algorithm Xiaoyu Wang, Patrick Avery, Davide Proserpio, Cormac Toher, Stefano Curtarolo, Eva Zurek

Thursday, March 7, 2019 8:48AM  9:00AM 
R17.00003: Meta GGA (SCAN) + van der Waals functionals (rvv10) calculation for Kedge Xray Raman Spectrum of the epsilon and zeta phase of solid oxygen Le Anh, Masahiro Wada, Zhi Li, Hiroshi Fukui, Toshiaki Iitaka Previous theoretical studies could not predict precisely the epsilonzeta transitional pressure which was measured at 96 GPa by experiments (Weck et al., PRL 2009, 102, 255503). The GW calculation showed the transitional pressure at 50 GPa (Kim et al., RPRB 2008, 77, 092104) while the B3LYP hybrid functional could estimate the coexistence range of epsilonzeta from 75 GPa to 145 GPa (OchoaCalle et al., PRB 2015 92, 085148). The combination of meta GGA(SCAN) and van der Waals functional (rvv10) was demonstrated to enhance the direct epsilonzeta transition at 70 GPa while the lattice parameters were very closed to the experimental data (in manuscript). On the other hand, the Inelastic Xray Scattering (IXS) was successfully used to study epsilon phase of solid oxygen (Meng et al., PNAS 2008, 105, 33). In this talk, we will discuss the evolution of calculated IXS Kedge spectra from epsilon phase to zeta phase using SCAN+rvv10. The calculated spectra will be compared to the experimental data. 
Thursday, March 7, 2019 9:00AM  9:12AM 
R17.00004: Dynamic nonequilibrium chemical bonding pathways under thermomechanical compression Anguang Hu The most urgent need in the explosion science of chemical reactions is about timeresolved nonequilibrium processes on when and how mechanical work and thermal heat are deposited into molecules to initiate reactions. Using quantum solidstate chemistry calculations, multiresolution and multiscale dynamic nonequilibrium simulations were recently developed for chemical reactions under compression. The nonequilibrium reaction processes are characterized by the lowest resolution in reactant and resultant conformations, the intermediate resolution in energy, enthalpy, mechanical stress, and chemical shear flows, and the highest resolution in reactive modes selected by compression. The dynamic motion of these flows is governed by a number of equations with respect to time, including the conservation of momentum and energy together with effects of mechanical endothermic bond compression, thermal heat transfer, and exothermic energy release of bond breaking related to irreversible Arrhenius kinetics with volume change and energy barriers. It provides details of dynamic nonequilibrium chemical bonding pathways from quantum to continuum scales. Simulations agreed well with experimental observations such as shock compressed graphite transformed into hexagonal diamond. 
Thursday, March 7, 2019 9:12AM  9:24AM 
R17.00005: phq: a Fortran code to compute phonon quasiparticle properties and dispersions Zhen Zhang, DongBo Zhang, Tao Sun, Renata Wentzcovitch Intrinsic thermal shifts of phonon frequencies due to lattice anharmonicity may be significant in solids at high temperatures. As such, the calculation of phonon dispersions incorporating anharmonic effects is critical for predictive studies of vibrational, thermodynamic, and lattice transport properties. Here we introduce the phq code to compute anharmonic phonon dispersions of crystals that combines molecular dynamics (MD) and lattice dynamics calculations. The method invokes the concept of phonon quasiparticles to extract thermal shifts and phonon lifetimes from velocity autocorrelation functions projected into normal modes sampled by MD simulations. With the renormalized frequencies, it is possible to construct an effective harmonic force constant matrix that allows us to calculate the anharmonic phonon dispersion over the whole Brillouin Zone. Due to the nature of phonon quasiparticles, this approach is applicable not only to simply crystals, but also to complex crystal structures with many atoms per primitive cell with extra effort. We demonstrate successful applications of this code to weakly and strongly anharmonic systems. In addition to temperaturedependent anharmonic phonon dispersions, the vibrational entropy and free energy at constant volume can also be obtained. 
Thursday, March 7, 2019 9:24AM  9:36AM 
R17.00006: Evolutionary optimized PAW (EPAW) datasets across the periodic table Kanchan Sarkar, Natalie A Holzwarth, Renata Wentzcovitch <div>We have recently designed and implemented a method named “Evolutionary Generator of projector augmented wave datasets” (EPAW1.0) [1,2] to produce optimized projector augmentedwave (EPAW) datasets. The generated EPAW datasets are transferable and can be employed in Quantum ESPRESSO and ABINIT distributions for the accurate prediction of materials properties at the scalar relativistic level. The accuracy level is very close to the highly precise calculations by the allelectron full potential linearized Augmentedplanewave (AEFLAPW) approach as implemented in the WIEN2k code. The EPAW performance level in solidstate studies is nearly uniform over an enlarged pressure region and outperforms other standard PAW dataset libraries, ultrasoft, and normconserving pseudopotentials mentioned in the reported effort by Lejaeghere et al. [3]. Employing EPAW1.0, we generate both LDA and GGA EPAW libraries especially for lowpressure calculations for elements across the periodic table. 
Thursday, March 7, 2019 9:36AM  9:48AM 
R17.00007: qha: A Python package for quasiharmonic free energy calculation for multiconfiguration system Qi Zhang, Tian Qin, Koichiro Umemoto, Renata Wentzcovitch The quasiharmonic approximation (QHA) offers an effective way of calculating the thermodynamic properties of many crystalline solids at high pressures and temperatures. In some cases, e.g., solid solutions or partially disordered systems such as H_{2}O iceVII, the system has numerous symmetrically distinct configurations. Here we present a Python package, qha, which can calculate the equation of state and various thermodynamic properties of both single and multiconfiguration crystalline systems in the framework of the QHA. This code has a wide range of applications, including, but not limited to, orderdisorder phase transitions ^{[1]}, solid solutions ^{[2]}, complex defect stability ^{[3]}, etc. Apart from its versatility, qha has been tested to be both accurate and computationally efficient. It can also be used as an allinone executable or taken apart into standalone functions, increasing its usability. 
Thursday, March 7, 2019 9:48AM  10:00AM 
R17.00008: Intrinsic Lattice anharmonicity and thermal conductivity of PbTe at High Temperature: Breakdown of the Phonon Minimal Mean Free Path Theory XingJu Zhao, DongBo Zhang, Yong Lu, Tao Sun

Thursday, March 7, 2019 10:00AM  10:36AM 
R17.00009: Thermodynamics and Thermal Conduction at Extreme Conditions Based on Phonon Quasiparticles Invited Speaker: DongBo Zhang Predictions of materials properties at extreme conditions of pressures and temperatures are exceedingly important because it is challenging to obtain them experimentally. At the atomistic level, the accuracy of these predictions relies essentially on a satisfactory characterization of lattice anharmonicity which is generally pronounced at high temperatures. This has stimulated the development of several ab initio approaches to address anharmonic effects on lattice vibrations. 
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