First principles modeling of mechanical properties of binary alloys containing Ga, Sn, and In for soldering applications.

Using density functional theory, the elastic properties of various binary Ga, Sn, and In-based alloys have been calculated to determine their viability as potential replacements for toxic Pb-based solders. Computed quantities such as the bulkK, shearG, and Young'sEmoduli were used to evaluate the mechanical behavior of the studied materials. The Pugh ratioγand Poisson's ratioνwere utilized to quantify the ductility of the alloys. Through comparative charge density analysis, we illustrated the relationship between the relative charge distributions and the aforementioned ductility metrics. Among the 52 studied alloys, 27 were determined to be stable/metastable at room temperature, and each of these stable/metastable materials are expected to be ductile. To facilitate the discovery and implementation of thermodynamically accessible and ductile solders, this work focuses on the mechanical properties of the alloys expected to be stable/metastable. Based on the cutoff criteria for stability and ductility established at the end of this work (EForm<10 meV/atom andγ > 4.00), theα-Ga0.125In0.875, GaII0.750In0.250, GaII0.833Sn0.167and In0.875Ga0.125alloys warrant further study for soldering applications.

Modified Born method for modeling melting temperature usingab initiomolecular dynamics.

The prediction of a material's melting point through computational methods is a very difficult problem due to system size requirements, computational efficiency and accuracy within current models. In this work, we have used a newly developed metric to analyze the trends within the elastic tensor elements as a function of temperature to determine the melting point of Au, Na, Ni, SiO2and Ti within ±20 K. This work uses our previously developed method of calculating the elastic constants at finite temperatures, as well as leveraging those calculations into a modified Born method for predicting melting point. While this method proves to be computationally expensive, the level of accuracy of these predictions is very difficult to reach using other existing computational methods.

Simulating dielectric spectra: A demonstration of the direct electric field method and a new model for the nonlinear dielectric response.

We demonstrate a method to compute the dielectric spectra of fluids in molecular dynamics (MD) by directly applying electric fields to the simulation. We obtain spectra from MD simulations with low magnitude electric fields (≈0.01 V/Å) in agreement with spectra from the fluctuation-dissipation method for water and acetonitrile. We examine this method's trade-off between noise at low field magnitudes and the nonlinearity of the response at higher field magnitudes. We then apply the Booth equation to describe the nonlinear response of both fluids at low frequency (0.1 GHz) and high field magnitude (up to 0.5 V/Å). We develop a model of the frequency-dependent nonlinear response by combining the Booth description of the static nonlinear dielectric response of fluids with the frequency-dependent linear dielectric response of the Debye model. We find good agreement between our model and the MD simulations of the nonlinear dielectric response for both acetonitrile and water.

Ab initio investigation of the temperature-dependent elastic properties of Bi, Te and Cu.

Using density functional theory and ab initio molecular dynamics, we have investigated the elastic properties of Bi, Te and Cu as a function of temperature. We compare calculated quantities which can be used to determine the effectiveness of our proposed method, such as the bulk (K), shear (G), and Young's (E) moduli. We also computed Poisson's ratio (ν) and the Pugh ratio (γ) for each of these materials at different temperatures to investigate changes in ductility. We have used the elastic moduli to calculate the Debye temperature θ D and minimum thermal conductivity k min of these materials as a function of temperature. We found that the elastic properties calculated in this work are in good agreement with experimental work. The inclusion of temperature effects has allowed for the proper prediction of ductility for each of these materials, a feat that standard density functional theory calculations has previously been unable to accomplish for Bi and Te.