Title:

Building novel material models using ab-initio data-driven frameworks

Speaker:

Dr. Svetoslav Nikolov

Affiliation:

Sandia National Laboratories

When:

Monday, November 14, 2022 at 1:00:00 PM   Add to Calendar

Where:

MRDC Building, Room 4211

Host:

Alexander Alexeev
alexander.alexeev@me.gatech.edu
4043853659

Abstract

In ferromagnetic materials like iron, spin-orbit coupling effects can have a strong impact on the underlying mechanical response and phase stability. Hence an adequate resolution of the magnon and phonon dynamics is critical for accurately predicting the material properties of ferromagnets over large regions of the temperature/pressure phase-space. In the current seminar I will discuss how we can utilize finite-temperature ab-initio calculations for iron to train a spectral neighbor analysis potential (SNAP) along with a bi-quadratic exchange Hamiltonian to resolve the magnon/phonon dynamics within a molecular-spin dynamics (MSD) framework. In our MSD framework we also include a Neel interaction model which enables us to capture the magnetostrictive coefficients at finite temperature. To test the validity of our MSD model we first measure the elastic, thermal, and magnetic response in the 0-1200K range at ambient pressure. To characterize the magnetic response, we apply a series of spin rotation to probe how the magnetocrystalline anisotropy varies with temperature. Meanwhile, to measure the thermal response of iron we perform non-equilibrium molecular-spin dynamics (NEMSD) simulations which enable us to separately calculate magnon and phonon conductivities. After this, we test how the MSD model for iron performs at high-energy density (HED) conditions by carrying out large-scale shock simulations, up to earth-core conditions. Doing this we gauge the impact of longitudinal spin fluctuations on the bcc-hcp transition and melt line under shock. Using sub-samples of the predicted MSD shock states at earth-core conditions we measure the corresponding viscosity and electronic conductivity (via DFT).

Funding statement: Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Biography

Svetoslav Nikolov is a Woodruff School of Mechanical Engineering alumnus, who obtained his Ph.D. in 2020, while working in Alexander Alexeev’s Complex Fluids Modelling and Simulation (CFMS) group. Currently he is a senior member of the technical staff in the Center for Computing Research (CCR) at Sandia National Laboratories. His research focus is geared towards leveraging data-driven frameworks for building mesoscale material models.

Notes

Refreshments will be served.