Q-POP-IMT: Phase-field module for modeling coupled insulator-metal transitions (IMT) and mesoscale structural evolution

Many strongly correlated quantum materials exhibit an insulator-metal transition, which enables various promising applications such as field-effect transistors without doping and neuromorphic computing. These real applications and experiments usually involve mesoscale, nonequilibrium, and inhomogeneous physical processes in quantum materials, which are difficult for microscopic first-principles theories to address. We developed an open-source package called Quantum Phase-field Open-source Package – Insulator-Metal Transitions (Q-POP-IMT), which implements the phase-field model of insulator-metal transitions capable of simulating mesoscale, nonequilibrium, inhomogeneous processes of insulator-metal transitions and their associated electronic and structural responses. The package is based on the finite-element method that supports complex boundary conditions corresponding to real systems.

Q-POP-FerroDyn: Coupling of Electron-Phonon-Photon Dynamics in Ferroelectric Materials

Understanding and predicting the coupled dynamics of electrons, phonons, and photons in condensed matter is of fundamental importance to the design and application of a wide variety of functional and quantum materials. For example, the coupled dynamics of free carriers (electrons and holes), strain (acoustic phonons), polarization (optical phonons), and electromagnetic waves (photons) underpins the optical excitation of ferroelectric crystals and polar semiconductors (e.g., III-V nitride) materials, with applications in a wide range of acoustic, photonic, and quantum devices. As an initial focus, we are developing an open-source package called Quantum Phase-field Open-source Package – Dynamics of Ferroelectrics (Q-POP-FerroDyn), which implements a dynamic phase-field model that uniquely allow for mesoscale simulation of the coupled mode dynamics in ferroelectric materials of arbitrary geometry and spatially inhomogeneous polarization patterns under various mechanical boundary conditions. The package provides a much-needed connection between the rapidly developing ab initio methods of coupled fundamental modes in quantum materials and the multimodal ultrafast spectroscopic and imaging methodologies. The package will support highly scalable graphics processing unit (GPU) based parallelization from single GPU in PCs and laptops to peta- and exascale supercomputers with thousands of GPUs, and thus should enjoy widespread download and reuse in the field of ferroelectrics and polar semiconductors.

Under developments

Q-POP-Supercon: Phase-Field Module for Superconducting Phase Transition and Mesoscale Vortex Pattern Formation in the presence of strain, polarization, and defects

The Ginzburg-Landau theory for superconductivity has been widely successful in describing the phenomenology of the superconducting phase transition and serves as an excellent starting point for exploring the coupled dynamics of the superconducting phase transitions. We developed phase-field model and module for simulating the superconducting phase transitions and mesoscale vortex pattern evolution in the possible presence of a magnetic field, ferroelectric polarization, and charged defects on vortex pinning, as well as the dynamical effect of applied optical field.

Under development

Q-POP-Diffraction: A Software Module to Computer Diffration Patterns of Phase-field Simulated Microstructures

The diffraction pattern of a material contains vital information about the crystal structures of underlying phases, grains, and ferroic domains. While diffraction patterns have been used for many years in an experimental setting, mesoscale microstructural models, such as phase-field, naturally reproduce real-space images of spatial distribution of these phases, structural, and ferroic domains. We have developed an approach to directly compute crystal diffraction patterns of microstructures predicted by phase-field simulations. This now enables researchers to study to predict the diffraction pattern of structural domains (like twin structures), ferroelectric vortices, and polycrystalline grain distributions to allow for direct comparison with experimental results, greatly enhancing the synergy and capabilities of mesoscale modeling.

To be released

#SHAARP-si: Analytical and Numerical Modeling of Optical Second Harmonic Generation in Anisotropic Crystals

Electric-dipole optical second harmonic generation (SHG) is a second-order nonlinear process that is widely used as a sensitive probe to detect broken inversion symmetry and local polar order. Analytical modeling of the SHG polarimetry of a nonlinear optical material is essential to extract its point group symmetry and the absolute nonlinear susceptibilities. Current literature on SHG analysis involves numerous approximations and a wide range of (in)accuracies. We have developed an open-source package called the Second Harmonic Analysis of Anisotropic Rotational Polarimetry (♯SHAARP.si) which derives analytical and numerical solutions of reflection SHG polarimetry from a single interface (.si) for bulk homogeneous crystals with arbitrary symmetry group, arbitrary crystal orientation, complex and anisotropic linear dielectric tensor with frequency dispersion, a general SHG tensor and arbitrary light polarization. ♯SHAARP.si enables accurate modeling of polarimetry measurements in reflection geometry from highly absorbing crystals or wedge-shaped transparent crystals. The package is extendable to multiple interfaces.

The interested researcher can learn more about the software at the following link.

#SHAARP.ml: Optical Second Harmonic Generation in Anisotropic Multilayers with Complete Multireflection Analysis of Linear and Nonlinear Waves

Optical second harmonic generation (SHG) is a nonlinear optical effect widely used for nonlinear optical microscopy and laser frequency conversion. Closed-form analytical solution of the nonlinear optical responses is essential for evaluating the optical responses of new materials whose optical properties are unknown a priori. A recent open-source code, SHAARP(si), can provide such closed form solutions for crystals with arbitrary symmetries, orientations, and anisotropic properties at a single interface. However, optical components are often in the form of slabs, thin films on substrates, and multilayer heterostructures with multiple reflections of both the fundamental and up to ten different SHG waves at each interface, adding significant complexity. Many approximations have therefore been employed in the existing analytical approaches, such as slowly varying approximation, weak reflection of the nonlinear polarization, transparent medium, high crystallographic symmetry, Kleinman symmetry, easy crystal orientation along a high-symmetry direction, phase matching conditions and negligible interference among nonlinear waves, which may lead to large errors in the reported material properties. To avoid these approximations, we have developed an open-source package named Second Harmonic Analysis of Anisotropic Rotational Polarimetry in Multilayers (SHAARP(ml)). The reliability and accuracy are established by experimentally benchmarking with both the SHG polarimetry and Maker fringes predicted from the package using standard materials.

Q-POP-Thermo

A new computational tool, which we have named Q-POP-Thermo, was developed for providing a fast assessment on the possible equilibrium states of structural/electronic domains and their respective volume fractions for bulk, thin films, and complex heterostructures under given thermal, electric, and mechanical conditions. This tool is more efficient than full-scale state-of-the-art phase-field simulations which can help to pinpoint phase-field simulations. Therefore, this software can provide researchers a quick initial assessment of the possible thermodynamic states of a material before carrying out full-filed expensive phase-field simulations of mesoscale domain pattern evolution.

The software is licensed under the MIT license.

Additional modification and enhancements to the code are in the pipeline which include multi-domain structures, Metal-Insulator transitions, and chemical thermodynamics.

 

BoltzTraP2Y: Atomic to Mesoscale Bridging

We developed a preliminary package to bridge the scale gap between DFT results and larger-scale simulation methods like phase-field modeling, named BoltzTraP2Y, based on previous work and the open-source software BoltzTraP2. The package takes input from DFT calculations and existing DFT databases, and calculates equilibrium chemical potential and heat capacity of electrons, as well as provides the kinetic properties including charge carrier mobility and electrical and thermal conductivities by solving the Boltzmann transport equation. We have already implemented this package to help understand various phase transitions in which the material undergoes an electronic structure change, like metal-insulator transitions. As an example, we calculated the thermodynamic and kinetic properties of Ca₃Ru₂O₇ as an input, which yield reasonable results agreeing well with previous experimental reports. This data were further used for phase-field simulations of light-excited electron dynamics. Ultimately, the package should prove essential in expanding the power of computational materials research by bridging the critical spatial scale gap among various methods and providing valuable assistance in parametrization of phase-field models.

We have received well-regarded reviews of the software. Some of which are shown below.

“Recently we used your modified code to calculated the FeNbSb half-Heusler thermoelectric properties. We found that the electrical conductivities agree with the experimental ones very well, when using the relaxation time, based on your code. Both the tau(s) and    tau_1(s) work well” Dr. Rundong (Kunming University of Science and Technology, China)

 

DFFTK: Density Functional Theory Tool Kit

We worked in collaboration with two other groups at Penn State and developed a distribution of high-throughput first-principles calculation software in Python termed DFTTK. The package integrates our experiences on first-principles theoretical method and the wealth of computational software developed over the past decades. It works well with submitting DFT tasks on all popular operating systems as well as adequately performing the DFT calculations on Linux systems. We have implemented cloud calculation functions from PyMatGen and Atomate which have been developed previously. It is expected that these calculations will prove useful for researchers seeking to understand the structure and properties of materials at finite temperatures to aid in the materials by design paradigm.

PyVecAnalysis: A Software Module for Automated Identification of Topological Structures

To accelerate and standardize the analysis of topological structures, such as the polar vortices and skyrmions in  PbTiO₃/SrTiO₃ superlattices, we developed a tool that utilizes the vector decomposition techniques, such as the Helmholtz-Hodge decomposition, to computationally identify vortices and other novel domain structures in complex heterostructures, such as skyrmions and hedgehog topological states. It is believed that such decomposition and identification techniques will lead to quicker high-throughput studies of these interesting structures for engineering applications.

The software is licensed with the MIT license. A module is being developed that will be directly implemented into the Q-POP code as it is developed.