Construct phonon tight-binding model and calculate its topological properties. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again. Skip to content. Construct phonon tight-binding model and calculate its topological properties woohyunhan.
Dismiss Join GitHub today GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together.
Branch: master. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Git stats 36 commits 1 branch 0 tags. Failed to load latest commit information.
View code. Han and K. About Construct phonon tight-binding model and calculate its topological properties woohyunhan. Releases No releases published. You signed in with another tab or window.Description: This tag is used in the the evaluation of the Berry phase expression for the electronic polarization of an insulating system.
As of VASP. In addition, the following keywords must be specified in order to generate the mesh of k-points:. DIPOL specifies the origin with respect to which the ionic contribution to the dipole moment in the cell is calculated.
When comparing changes in this contribution due to the displacement of an ion, this center should be chosen in such a way that the ions in the distorted and the undistorted structure remain on the same side of DIPOL in terms of a minimum image convention.
Calculations 5 to 8: To calculate the change in the electronic polarization of NaF due to the displacement of the fluorine sublattice, one should repeat Calculations 1 to 4, using the following POSCAR file:. This corresponds to a displacement of the F ion by 0. Collecting the results: The change in the electronic contribution to the polarization due to the F-sublattice displacement should be calculated as follows:. Considering that the moved F-sublattice was displaced by 0. More information on this particular aspect of the Berry phase calculations can be found in references      .
Examples that use this tag. An example: The fluorine displacement dipole Born effective charge in NaF First one needs to determine the electronic polarization of the undistorted NaF. King-Smith and D. Vanderbilt, Phys. B 47, Vanderbilt and R. King-Smith, Phys. B 48, Resta, Ferroelectrtics51 Resta, Rev.
King-Smith, in Electronic polarization in the ultrasoft pseudopotential formalism, Unpublished report, Within the context of the ultrasoft pseudopotential USPP formalism of Vanderbilt [ 1 ], the electronic contribution to the macroscopic polarization can be decomposed into two terms [ 2 ]. The overlap matrix is given by. The second term on the right-hand side of Eq. The presence of the second term in Eq.
It is called the "expectation-value" EV term, since it takes the form of a conventional expectation value, and is given by. In the following we will relate the quantities necessary to evaluate Eqs. The cell-periodic part of the Bloch function is easily found from the coefficients in the plane wave expansion of.
The first term on the right-hand side of Eq. The projections are performed in reciprocal space. Analogous to Sec. Adopting definition Note: the calculation of this projection in VASP does not include the factorbecause only expressions of the form occur. Therefore we need not evaluate Eq.
The matrix is handled differently, since it contains ketswhich are not obtained from an independent diagonalization but are found through see Sec. Usingwe obtain the following equations to replace Eqs.Obtains the package. Please email lizhi for detail. Prerequisitions: First principles methods that can accurately calculate force on atoms.
We use VASP as default package. Program Details. Because of the enormous number of intermediate files generated during the Gibbs Free energy calculation, GPT package maintains a tree-like structure under each job.
The following diagram illustrates the tree structure.
Berry phases and finite electric fields
The bold letter indicate the file name used in the calculation. The extension name indicates the purpose of the job. The reason to have a different input file for each type of calculation is that different type of calculation may require different accuracy setting and k-point sampling.
For example, for optical dielectric tensor calculation, a much large set of k-points may be required to obtain sufficient accuracy. On the other hand, for Berry phase calculation, a medium fine k-point mesh and accuracy would be sufficient.
The main problem with this approach is that there are a large set of input file needs to be prepared and maintaining the consistency among the input files is not straightforward. This is the temperature parameter used to calculate the Fn V,T curve. This is the k-point sampling for phonon DOS calculation. Number of K-point per phonon dispersion segments.
Several enhancements have been added to the original PHON program: Symmetry analysis of zone center phonon modes. A special k-point set has been generated for each lattice type. Generated by phon program FREQ. MgO: MgO is an ionic crystal with a simple crystal structure. GPT is a very computation intense package. Parallelization at batch job level is a very important direction for improving its performance.
In fact, many tasks, here a task referring a first principles calculation, are easy-parallelizable tasks that require virtually no-inter communications among individual tasks.
For example, force calculations after small perturbations from the equilibrium position. Each force calculation is complete independence task and there is no inter-dependence between each force calculations. I am currently evaluating the two solutions: a parallel job queuing system.Calculating the change in dipole moment per unit cell under PBC's, is a nontrivial task.
We will briefly summarize the essential results for a review of geometric quantum phases in polarization theory see the papers of Resta  . Central to the modern theory of polarization is the proposition of Resta  to write the electronic contribution to the change in polarization due to a finite adiabatic change in the Kohn-Sham Hamiltonian of the crystalline solid, as.
The physics behind the equation above becomes more transparent when this expression is written in terms of the Wannier functions of the occupied bands. This indeterminacy stems from the fact that the charge center of a Wannier function is only invariant modulo Rwith respect to the choice of phase of the Bloch functions.
As of version 5. The second term on the right-hand-side of the electric enthalpy functional introduces a corresponding additional term to the Hamiltonian. Following the work of Nunes and Gonze  we write. Note : One should be aware that when the electric field is chosen to be too large, the electric enthalpy functional will lose its minima, and VASP will not be able to find a stationary solution for the field-polarized orbitals.
This is discussed in some detail by Souza et al. If one does not include unoccupied bands, VASP is obviously not able to determine the bandgap and can not check whether the electric field might be too large. This will also produce a warning message. Examples that use this tag. Vogl, J. C: Solid State Phys. King-Smith and D. Vanderbilt, Phys. B 47, Resta, Ferroelectrics51 Resta, Rev.
Monkhorst and J. Pack, Phys. B 13, Nunes and X. Gonze, Phys. B 63, Souza, J. Categories : Dielectric Properties Berry phases Theory. Page actions Page Discussion More Tools. Personal tools Log in.Calculated total magnetic moment for the unit cell within the magnetic ordering provided see below.
Typically accurate to the second digit. Calculated formation energy from the elements normalized to per atom in the unit cell.
Stability is tested against all potential chemical combinations that result in the material's composition. In general, band gaps computed with common exchange-correlation functionals such as the LDA and GGA are severely underestimated. We additionally find that several known insulators are predicted to be metallic. Select an element to display a spectrum averaged over all sites of that element in the structure. Download spectra for every symmetrically equivalent absorption site in the structure.
Explore more synthesis descriptions for materials of composition TiPbO3. Text computed by synthesisproject. Note the primitive cell may appear less symmetric than the conventional cell representation see "Structure Type" selector below the 3d structure. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. Material Details Final Magnetic Moment 0. Density 8. Band Structure. Semi-local DFT tends to severely underestimate bandgaps.
Please see the wiki for more info. Interactive plots. Data 5 doi Interfaces 8 : doi Elasticity Reference for tensor and properties: Scientific Data 2 : doi Compliance Tensor S ij 10 Pa -1 4. Similar Structures Explanation of dissimilarity measure: Documentation. Up to 5 similar elemental, binary, ternary, quaternary, etc. E hull : energy above hull per atom [eV]. Synthesis Descriptions Ceramic samples of PFN and 0.
These oxides were batched in stoichiometric [ Calculation Summary Elasticity Methodology.
How do we arrive at this value? This ensures that calculations performed using different InputSets are not compared against each other.Calculate bulk energy band for a series k lines.
This is the basic calculation after the construction of Wannier functions. You have to compare your Wannier interpolated bands with the DFT bands. Those two bands should match well around the Fermi level. The outputs for bulk band calculation are bulkek. You can get the band plot by running. You have to set the following tags in wt. You can plot the Dirac cone with matlab. Column rd are k points in cartesian coordinates.
Column th are k points in a rotated cartesian coordinates where the x and y direction are line in the k plane and the z direction is perpendicular to the k plane you specified. Column th are energies at each k point. Here we only print out 4 energy bands around the fermilevel. It depends on NumOccupied. Usually, I choose column 4th and 5th as k coordinates and choose 8 and 9 as energy bands to show the Dirac cone shown below.
The outputs for this function are FS3D. You can plot the FS with xcrysden run. Calculate spin texture for bulk system that with vacuum or without inversion symmetry. For the bulk system with vacuum, you can calculate the surface projected spin texture. In this case, you have to do the first-principle calculations for a finite thickness slab system that with vacuum.
Outputs are dos. We support two modes for energy gap calculations. This is useful to show Weyl points and nodal line structure. The GapPlane. The GapCube. Otherwise, it will become very time consuming. Outputs are Nodes.
After you identify the positions of Weyl points, you could use this function to calculate the chirality, which tells you whether a Weyl point is a sink or a source of the Berry Curvature.