Using density functional theory to construct multiphase equations of state: tin as an example

Abstract

We present a general methodology for using density functional theory (DFT) calculations as a basis for constructing multiphase equations of state (EOS). Focusing on tin as an example, we discuss the full process of generating a tabular EOS, starting from first-principles calculations and arriving at a full EOS in agreement with existing experimental data. We begin by describing DFT calculations for the five solid phases and liquid phase of tin, including cold curve, phonon, and DFT-based molecular dynamics calculations. We then discuss methods for incorporating DFT results into materials models used in OpenSesame, the program used to create a full tabular multiphase EOS. Next, we outline a general strategy for adjusting model parameters in OpenSesame to fit to a variety of experimental data, including isobaric data, isothermal data, shock data, solid-solid phase boundary measaurements, and measurements of the melt curve. We end with a discussion of the advantages of using DFT data as a foundation for EOS generation and discuss potential strategies for automated EOS generation based on the fitting process highlighted in this work.

Multiphase tin equation of state using density functional theory

“…Additional details and comparisons of the PBE and AM05 cold curve calculations are provided in Ref. 86.…”

“…Additional details regarding cold curve comparisons and the enthalpy are provided in Ref. 86, and comparisons of the room temperature 2162 isotherms to experimental DAC data are provided in Sec. III.…”

“…Above V ref , another form for Γ is used to prevent Γ from diverging in the expansion region well below solid densities, such that Γ → 1 as V → ∞ (see Ref. 86 for additional details).…”

“…While we only summarize the main results here, a more comprehensive description of the process used to incorporate DFT calculations into materials models used in OpenSesame, as well as a description of how model parameters are adjusted to fit to experimental data, is provided in Ref. 86.…”

OpenSesame tutorial

“…Note that a new tin EOS, SESAME 2162, has also been developed and includes 4 solid phases of tin [5,6], and therefore can be thought of as the successor to 2161. However, for tutorial purposes, it is easier to discuss the simpler case of just 2 solid phases.…”