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### Ab Initio and Electronic Structure

## Quantum Espresso DFT tools in nanoHUB

**Use this link to access all nanoHUB content related to Quantum Espresso**

This creates a tag search for Quantum Espresso. Filter the results using the menu on the right of the results.

**ABINIT**

**ABINIT**

**ABINIT** is a package whose main program allows users to find the total energy, charge density and electronic structure of systems made of electrons and nuclei (molecules and periodic solids) within Density Functional Theory, using pseudopotentials and a planewave basis.

**ABINIT** also includes options to optimize the geometry according to DFT forces and stresses, to perform molecular dynamics simulation using these forces, or to generate dynamical matrices, Born effective charges, and dielectric tensors.

In addition to the main ABINIT code, different utility programs are provided.

**MIT Atomic-Scale Modeling Toolkit**

The following simulations are run by the tool:

- Averages and Error Bars
- Molecular Dynamics (Lennard-Jones)
- Molecular Dynamics (Carbon Nanostructures and More)
- Monte Carlo (Hard Sphere) * Monte Carlo (Ising Model)
- Quantum Chemistry (GAMESS) * Density-Functional Theory (Quantum Espresso)
- Density-Functional Theory (SIESTA)
- Quantum Monte Carlo (QWalk)

**Berkeley GW**

**Berkeley GW**

This is an educational tool that illustrates the calculation of the electronic structure of materials using many-body perturbation theory within the GW approximation. This tool provides an introduction to many-body perturbation theory within the GW approximation as a method to compute the electronic structure of materials including exchange and correlation effects beyond those in standard density functional theory (DFT), such as the local density approximation, the generalized gradient approximation, or even hybrid functionals.

This tool contains two examples: bulk silicon and a gas-phase benzene molecule. It allows the user to calculate the quasiparticle band structure for the former and the molecular orbital energies of the latter. For both examples, the user can vary the convergence parameters and explore how they affect the accuracy.

**SIESTA**

**SIESTA**

**SIESTA** is a fast electronic structure program that uses a local basis. It can produce band structures and minimum energy geometries, and can perform first principles molecular dynamics calculations. ** siesta Website**

**nanoMATERIALS SeqQuest DFT**

**nanoMATERIALS SeqQuest DFT**

Powered by SeqQuest**nanoMATERIALS SeqQuest DFT** provides access to the density functional theory code SeqQuest via nanoHUB.org. SeqQuest is being developed at Sandia National Laboratories by Dr. Peter A. Schultz of the Multiscale Dynamic Materials Modeling Department and collaborators. Using SeqQuest enables users to calculate the total energy, atomic forces and stress for molecules, wires, slabs and bulk systems.

__QC Lab__

__QC Lab__

Powered by GAMESS

(Quantum Chemistry Lab) provides *Ab Initio* and DFT molecular and electronic structure calculations of small molecules.

__Strain Bands__

__Strain Bands__

Strain Bands uses first-principles density functional theory within the local density approximation and ultrasoft pseudopotentals to compute and visualize density of states, E(k), charge densities, and Wannier functions for bulk semiconductors. This tool can be used to explore the influence of strain on first-principles bandstructures of semiconductors.

__DFT Calculations with Quantum ESPRESSO__

__DFT Calculations with Quantum ESPRESSO__

DFT calculations with Quantum ESPRESSO enables nanoHUB users to run quantum ESPRESSO, a powerful electronic structure code. Users can perform total energy calculations, energy minimization to predict structures, obtain the Kohn-Sham band structure of periodic systems as well as phonons.

__DFT Materials Properties Simulator__

__DFT Materials Properties Simulator__

Materials modeling provides a cost and time efficient method for studying their properties, especially in nanotechnology where length and times scales are not accessible experimentally. Our research focuses on developing a tool useful for both instructional and research purposes that calculates materials properties. The tool relies on density functional theory (DFT) calculations to compute specific properties for a wide range of materials including semiconductors, insulators, and metals. A major goal with our tool was keep the GUI very simple for novice users, such as students, while retaining an advanced option section for experienced users, such as researchers. The tool can compute electronic band structures, density of states, bulk modulus, dielectric constants and other properties of the material. Furthermore, the user can select from various pre-set materials or create one of their own by specifying the atomic structure. The end-product we have built combines the simplicity of a teaching tool with the versatility of a research tool, resulting in a powerful simulation package.

**ab initio simulations with ORCA**

**ab initio simulations with ORCA**

The ORCA tool allows the user to perform ab initio simulations on molecular systems. The levels of theory range from post-Hartree-Fock methods to density functional theory including various functional and basis sets. The tool allows geometry optimizations with or without constrains, normal modes analysis and automatic ionization energy calculation.

Powered by ORCA an ab initio, DFT and semiempirical SCF-MO package from Max-Planck-Institute for Chemical Energy Conversion, Germany.

**The Basics of Quantum Monte Carlo**

__QWalk Quantum Monte Carlo Tutorial__

__QWalk Quantum Monte Carlo Tutorial__

QWalk Quantum Monte Carlo Tutorial uses Quantum Monte Carlo methods solve the Schrodinger equation for many electrons to high accuracy, in some cases exactly.

In most implementations, it also has favorable scaling with system size, approximately the same as mean-field theories like density functional theory, although with a larger prefactor. This allows us to obtain accurate ground and excited state energies for realistic chemical systems. Quantities such as binding energies, reaction barriers, and band gaps are accurately simulated using QMC methods.