Title:
Modeling pseudo-elasticity in small-scale ThCr2Si2-type crystals: Model data

Abstract:
Crystals of the ThCr2Si2-type structure comprise a large class of known compounds, and observations of superconductivity in some of the compounds generated significant interest in these materials. Recently, nano-indentation experiments have shown that at room temperature, small-scale crystals of CaFe2As2 exhibit pseudo-elastic behavior with recoverable strains of over 10%. These experiments also demonstrate the potential for shape memory effects at cryogenic temperatures, behavior which has previously been related to its magnetic phase transitions. In this work, the phase transitions of CaFe2As2 are investigated using density functional theory (DFT) in conjunction with analytical models. The models demonstrate that both uniaxial and hydrostatic loading can give rise to pseudo-elastic behavior. These models are then applied to LaRu2P2, which does not exhibit a magnetic phase change, but is still found to have a similar pseudo-elastic response. A suite of parameters useful in quantifying the complex responses of these compounds is presented and it is demonstrated that c-axis strain is the critical loading parameter in predicting the pseudo-elastic behavior. These results provide a method of connecting local chemical tuning to macroscopic behavior.

Contact Person:
Ian N. Bakst

Contact Email:
ian.bakst@colostate.edu

Location of Data collection:
in-silico. Fort Collins, CO

Time period of Data Collection:
from 2016-10-01 to 2017-10-26

File Information/Directory Structure:
	Contents:
		-model_data (directory)		### Folder of model output data
			-cafeas_hs_disp.csv	### CaFe2As2 hydrostatic compression displacement control model output
			-cafeas_hs_load.csv	### CaFe2As2 hydrostatic compression load control model output
			-cafeas_uni_disp.csv	### CaFe2As2 uniaxial compression displacement control model output
			-cafeas_uni_load.csv	### CaFe2As2 uniaxial compression load control model output
			-larup_hs_disp.csv	### LaRu2P2 hydrostatic compression displacement control model output
			-larup_hs_load.csv	### LaRu2P2 hydrostatic compression load control model output
			-larup_uni_disp.csv	### LaRu2P2 uniaxial compression displacement control model output
			-larup_uni_load.csv	### LaRu2P2 uniaxial compression load control model output
				
		-raw_data (directory)		### Folder of raw DFT compression data
			-cafeas_hs.csv		### Hydrostatic compression data of CaFe2As2
			-cafeas_uni.csv		### Uniaxial compression data of CaFe2As2
			-larup_hs.csv 		### Hydrostatic compression data of LaRu2P2
			-larup_uni.csv		### Uniaxial compression data of LaRu2P2

		-README.txt (this file)


Acronyms:
DFT= Density Functional Theory
hs= Hydrostatic Compression
uni= Uniaxial compression
larup= LaRu2P2 (Lanthanum Ruthenium Phosphide)
cafeas= CaFe2As2 (Calcium Iron Arsenide)

Variable Information:
Each file will have a 1 line header with descriptions of the columns.
Stress is in GPa
Energy is in eV
Lengths are in Angstroms
Magnetic Moments are in Bohr Magnetons

Methods:
Data from DFT simulations, VASP plane-wave basis code. PAW pseudo-potentials.
LDA XC functional used for larup, GGA-PBE XC functional used for cafeas
energy cutoff= 600eV, Monkhorst-Pack grid of 13x13x5. energy tolerance= 1.0E-5 (eV)

Software:
DFT calculations were performed with the Vienna Ab-initio Simulation Package (VASP) v5.4
Model calculations were performed in MATLAB 2017a


