
Title
Physicist 
Email
yang1@llnl.gov 
Phone
(925) 4244153 
Organization
Not Available
Research Interests
My primary research interest is to develop and apply efficient quantum simulation methods for equation of state and materials strength modellings under extreme conditions. The current research projects include quantum molecular dynamics (QMD) simulations for lowZ materials, transitionmetal oxides and actinides.
Quantum molecular dynamics simulations for equations of state modeling
The quantumbased theoretical framework for obtaining highpressure and hightemperature phase diagrams and multiphase equations of state (EOS) for metals treats cold, ionthermal, and electronthermal contributions to phase stability and the EOS separately. For d and felectron metals, however, there can be a high density of electronic states at the Fermi level, leading to a strong coupling between the ion and electronthermal components for temperatures as low as melt. This effectively leads to temperaturedependent forces on the ions. Consequently, the hightemperature phase diagram and EOS, the melt curve, and the liquid EOS can all be significantly affected. To treat the electrons and ions on an equal footing I have been developing rigorous abinitio QMD simulations for d and felectron metals, so the additional ionelectron coupling and temperaturedependent forces in question are rigorously treated [1]. The areas of interest for this work are: (i) the development of robust QMD algorithms and pseudopotentials to treat electrons at high temperature and density regimes; (ii) the study of important physical phenomena, including hightemperature phase stability [2, 3] , melting, and liquid structure for equation of state modelling [4]; (iii) the development of QMDbased electronthermal and ionthermal models.
Multiscale modeling of materials strength
The predictive modeling across length scales all the way from the atomic level to the continuum level to achieve a physicsbased multiscale description of mechanical properties such as plasticity, strength and other mechanical properties requires an accurate atomistic description of defect properties as input into higher lengthscale simulations such as 3D dislocation dynamics (DD) of singlecrystal plasticity at the microscale. Especially important is the accurate atomistic modeling of the structure, motion, and interaction of individual dislocations, as well as the accurate modeling of the relevant aspects of elasticity, including elastic moduli and the limits of elastic stability. To accomplish this task fully, one not only needs to understand the underlying qualitative mechanisms that control plastic deformation, but also needs to be able to calculate the quantitative parameters that will allow a predictive description of plasticity and strength properties in real materials under various conditions. The latter is particularly important in regimes where experimental data are scarce or nonexistent such as under the extreme conditions of pressure, temperature, strain, and strain rate of current interest to many modern applications. Especially interesting in this regard is the regime of high pressure, a regime in which dislocationdriven plasticity has been heretofore largely unexplored from a fundamental perspective. My contribution of this work is to help fill that void. Specifically, we elaborate here a predictive multiscale description of dislocation behavior and singlecrystal plasticity in bcc transition metals (e.g., Pb) over a wide range of pressures, ranging from ambient all the way up to many hundreds of gigapascals (GPa) [5].
References
 Anharmonicityinduced firstorder isostructural phase transition of zirconium under pressure, E. Stavrou, L.H. Yang, P. Söderlind, D. Aberg, H.B. Radousky, M.R. Armstrong, Physical Review B 98, 220101 (2018).
 Quantummechanical interatomic potentials with electron temperature for strongcoupling transition metals. J.A. Moriarty, R.Q. Hood, L.H. Yang, Physical Review Letters 108 (3), 036401 (2012).
 Hightemperature phonon stabilization of guranium from relativistic firstprinciples theory, P. Söderlind, B. Grabowski, L. Yang, A. Landa, T. Björkman, P. Souvatzis, O. Eriksson, Physical Review B 85, 060301 (2012).
 Equation of state of boron nitride combining computation, modeling, and experiment, S. Zhang et al. Physical Review B 99, 165103 (2019).
 Modeling laserdriven highrate plasticity in BCC lead, R.E. Rudd, L.H. Yang, P.D. Powell, P. Graham, A. Arsenlis, R.M. Cavallo, ..., AIP Conference Proceedings 1979, 070027 (2018).
Ph.D., Physics, University of California at Davis