Questions tagged [density-functional-theory]
For questions about simulations using Density Functional Theory.
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How can I solve the error in TRANSIESTA calculations? [duplicate]
Recently, I've been trying to calculate the transmission coefficients for the molecular junction (Au lattice - molecule - Au lattice) using SIESTA, TRANSIESTA, and TBtrans.
As you know, the procedure ...
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What is the best program to manipulate plane-wave DFT wavefunctions to calculate custom matrix elements?
For pedagogical reasons, I am looking for ways to calculate quantum-mechanical quantities such as $\langle m | \dot{m}\rangle, \langle m | \dot{n}\rangle, \langle m | \ddot{n}\rangle$ using ...
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How to calculate band gap alignment for different layers used in double perovskite solar cell?
I want to compare the electronic bands (VBM and CBM) of a double perovskite material with other layer using like transports both holes and electrons .I tried to calculate them, but the values I ...
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Relax calculation not converging
I am using a DFT+U+V approach and using a pseudohybrid
density functional for extended Hubbard Coulomb interactions along with GBRV ultrasoft pseudopotentials (PBEsol). This enables me to open a gap ...
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How to build input files to obtain vibrational and thermodynamic measurements using Quntum Espresso?
I'm working with a SiPOCa structure and I've already done the SCF, NSCF, DOS, BANDS, CHARGE DENSITY, FTIR and RAMAN calculations. Now I would like to calculate the vibrational and thermodynamic ...
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Error in the PH file for RAMAN and FTIR calculation
I am doing the Raman and FTIR calculations using quantum espresso, I ran the following codes
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vc-relax calculation not converging with some pseudopotentials
I am new to Quantum ESPRESSO and it's my first calculations with $\mathrm{CsPbBr}_3$ perovskite structure. I am trying to perform vc-relax calculations. The ...
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Is it neccessary to apply dipole corrections in TMD bilayers?
I am at the beginning of my PhD and I just learned about the dipole correction in ab-initio calculations. I have seen that it is used mainly when an electric field is applied to a system. But I have ...
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How to construct the input files to obtain the structural measurements using Quntum Espresso?
I'm working with a SiPOCa structure and I've already done the SCF, NSCF, DOS, BANDS, CHARGE DENSITY, FTIR and RAMAN calculations. Now I would like to calculate the structural measurements of this ...
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Supercell Elastic Constant
Suppose, that one wants to study a bulk structure which is doped by several impurities. More precisely, I want to calculate the elastic constants using a DFT code (VASP) by fitting stress to strain (...
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Formation Energy Calculations
How may I calculate each term of the formation energy equation using DFT?
I am assuming that for every software (i.e. Quantum ESPRESSO; Wien2k), the calculation procedure must be the same.
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Is there an Optimized Norm-Conserving Vanderbilt (ONCV) pseudopotential of Eu atom?
I'm currently searching for an Optimized Norm-Conserving Vanderbilt (ONCV) pseudopotential of Eu, which has a localized f-orbital. But no matter how much I search online, I can't find it.
There is an ...
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Simple Quantum Espresso-Phonon
I am completely new to material modelling. I am trying to calculate phonon frequency at X point for Aluminium fcc.
I picked an fcc lattice and displaced the atoms at x=0 by (+0.1) and those in x=0.5 ...
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Help with Geometry Optimization in CASTEP
I am a beginner in CASTEP simulation and I need some guidance on the general steps for geometry optimization. I have tried the following three approaches:
(1) Build unit cell > geometry ...
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Calculation of material properties
I am in process of learning some simulation codes. There some properties for a material which are input parameters. I want to know if DFT or other related codes can be used to calculate them for any ...
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Disappearing vacuum layer when relaxing bilayered hBN with VASP
I'm doing geometry optimization of bilayer h-BN, a 72-atom supercell (6x6x1) with vacuum thickness of 20 Å, and I set the parameters in INCAR as below:
...
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How to carry out HSE06+SOC band structure calculation using VASP?
I could not find any good source for this type of calculation. I'd be very appreciated if someone who is experienced with that to show it step by step
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The Dynamic Constant Matrix for the Green Function in the Thermal Conductance Calculation
When computing the thermal transmission coefficient, the green function needs to be computed first; for example, $G^{R}_{scattering\:region}=\left[\left(\omega+i0^{+}\right)^{2}I-D\right]^{-1}$, where ...
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Prerelaxation before AIMD with VASP
I am investigating a bulk structure by ab initio molecular dynamics (AIMD) implemented in VASP.
I was wondering, how to choose the initial geometry (= POSCAR file) to run the AIMD simulation. In the ...
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What should be the criteria of convergence over ENCUT?
For example, should a computation be considered to converge when the differences in energy per atom are smaller than a certain value?
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Dynamical Matrix for the Thermal Transmission Coefficient Calculation
The dynamical matrix for the thermal transmission coefficient calculation is written as follows:
$$D_{I\alpha,J\beta}(\overrightarrow{q})=\frac{1}{\sqrt{M_{I}M_{J}}}\sum_{b}K_{I\alpha,J\beta}(a,b)e^{i\...
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Struggling with Mixed Basis Set Inclusion for IRC Calculations
I'm trying to compute the IRC for a W complex, and I'm using Def2TZVP for W and 6-311G** for the rest of the atoms. However, when I include the mixed basis set, Gaussian 16 generates a syntax error.
I ...
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Difference of the Transmission Coefficient between Thermal and Charge Conductance by Nonequilibirum Green Function Method
The equation 57 in the reference [Jian-Sheng Wang, Jian Wang and J. T. Lu, Quantum thermal transport in nanostructures, Eur. Phys. J. B 62, 381 (2008)] explains the the transmission coefficient for ...
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Errors in CASTEP supercell geometry optimization
These are the errors when I run my supercell on material studio using CASTEP module.
I have tried decreasing k points and also increased the cutoff energy. Furthermore I deleted all the files related ...
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Confused About Convergence Values in Quantum ESPRESSO: Seeking Help with Unit Conversion
I'm using Quantum ESPRESSO in my calculations. And I'm a bit confused about the convergence for energy between two consecutive steps and the force allowed on each atom.
In my input file, I retained ...
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Can the Electron Charge Density (ECD) have negative values and why?
In certain charge densities I am getting negative values, in the place where the atomic cores would be. I do not have access to the vasp.xml or OUTCAR files, so there is no way to determine whether ...
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Is the one-electron reduced density matrix enough in DFT?
There is a conceptual mismatch in my personal understanding between the role of reduced density matrices in DFT and post-HF methods (possibly due to different discussions in textbooks), and I can not ...
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How to choose the best U value for studying the electronic properties?
I'm new to DFT+U and trying to understand how FeTiO3 works by looking at its electronic properties. But there's a big problem: when I use normal DFT, I can't get the w
right band-gap value.
How can I ...
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How may I analyze the oxidation state of any atom by analyzing the DOS plot?
I was doing DFT calculations using VASP of some transition metal compounds and plotted the density of states (DOS) along with the projected density of states (PDOS).
I am wondering how can someone ...
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Source for Hammett Parameters useable in QSAR model training?
I tried to create a QSAR (Quantitative Structure Activity Relationship) model for my thesis that tries to predict the melting points of certain ZIFs (Zeolitic Imidazolate Frameworks) based on relative ...
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Is it essential to include solvent cage effect in radical reactions?
My question is straightforward and is outlined in the post title: Is it essential to include the solvent cage effect in radical reactions during the computational estimation of Gibbs free energies and ...
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What do Negative Atomic Orbital Contributions in a Mulliken Population Analysis mean?
I am performing a Mulliken population analysis (MPA) for a molecular system of interest (calculated with B3LYP/Def2-TZVP). I am analyzing the LCAO-MO coefficients/contributions associated with each &...
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How to choose the correct ibrav value and Identifying the 3-fold Axis
I'm trying to perform relaxation calculations for FeTiO3 with the ilmenite structure in Quantum Espresso. The documentation mentions two possible ibrav values for triagonal systems: 5 and -5. However, ...
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Temperature effect on electronic properties
I'm particularly interested in studying how temperature affects electronic properties. However, I've been working with Quantum Espresso and its DFT + U functionality, and I'm struggling to understand ...
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SCF calculations for new materials with unknown properties (e.g. charge, spin, magnetization) using Quantum Espresso
Performing SCF calculations for crystal structures using Quantum Espresso sometimes gives me this error.
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vdW Corrections for Comparing the Effects on Small Molecule Adsorption
Is it necessary to perform a new geometric relaxation with vdW corrections enabled for each implementation (DFT-D2, DFT-D3, etc.) when comparing their effects on the adsorption of small molecules on a ...
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pyscf: Why should the choice of pseudopotential determine the total energy, and not the physics?
I have limited experience with DFT, but as an exercise I have written a DFT program of an atom (from scratch using nothing more than python built in functions and numpy) by following Richard Martin's ...
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Help with understanding the method of MBD & MBD-NL
I am having a hard time understanding the steps of Tkatchenko's method of many-body dispersion (MBD) and nonlocal many-body dispersion (MBD-NL).
I would greatly appreciate a detailed & clear ...
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Frequency calculation using Quantum Espresso
I want to calculate the frequency using quantum espresso. How can I get the input file of frequency calculation using QE?
...
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How may I verify that my A matrix for TDA (Tamm-Dancoff Approximation of TD-DFT) from PySCF is correct?
This is a follow-up to a series of questions that I have asked here:
Is a D-Wave quantum computer able to do TD-DFT calculations? (answer was "yes, but it might not be efficient")
Inquiry ...
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Electronic Convergence issues for DFT+U+SOC in VASP for magnetic materials
While performing DFT+U+SOC calculation in VASP for the material $\mathrm{Mn_3Sb}$ my calculation is not at all converging. Here I am attaching the necessary input files. I have come across some ...
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Degenerate local-orbital radial functions
I am trying to do a simple groundstate calculation with the exciting code for a perovskite structure with 4d-electron elements. The code uses a muffin-tin approach and expands the wavefunctions inside ...
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Synergy of Exchange and Correlation, Why are they Combined in the Term "Exchange-Correlation" Energy
The exchange interaction is a quantum mechanical effect that only occurs between identical particles. The effect is due to the wave function of indistinguishable particles being subject to exchange ...
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Can I define molecular units on NBO3.1 or NBO6.0?
I'm studying donor-acceptor charge transfer (CT) process between tetrakis(m2-acetato)-di-Wolframium (acceptor) with an acetonitrile (donor) at the B3LYP-D3BJ/def2-TZVPD level of theory.
The W···N ...
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What are some pros/cons of Quantum ESPRESSO and FLEUR?
I want to know the pros/cons of plane wave (PW) pseudopotential (PP) based DFT codes and all-electron full-potential linearised augmented-plane wave (FLAPW) DFT codes. In the title, I mentioned ...
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Modeling techniques for simulating the electronic and structural properties of Transition Metal Dichalcogenide nanotubes
Dear Matter Modeling Stack Exchange community,
I am currently working on calculating the electronic and structural properties of Transition Metal Dichalcogenide (TMD) nanotubes using DFT, with a ...
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Error in TranSIESTA: "The electrode down-folding region is 0 in the device region"
When I run a tranSIESTA calculation, the SCF converges, and the TBtrans output shows the following error:
...
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Self-interaction in density functional approximations for many-electron systems
In their famous paper Self-interaction correction to density-functional approximations for many-electron systems Perdew and Zunger said
The exact density functional for the ground-state energy is ...
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Predicting the band gap or some other properties of materials before running any calculations [closed]
Can we somehow predict what sort of modulation doping will do to a material without actually running any calculations? For instance, could we use the already known density of states (DOS) of Zn to ...
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About Van der Waals (vdW) correction in VASP
I would like to know when we need to apply Van der Waals (vdW) correction in our system. If I am dealing with 2d systems (monolayer or bilayer), then should I need to add IVDW (vdW (dispersion) ...
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