Questions tagged [electronic-structure]
For questions concerning electronic structure concepts and calculations.
202
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Siesta: screening layer problem when the electrodes were made by placing a few layers of metal on top of a semiconductor monolayer
The electrodes were made by placing a few layers of metal on top of a semicondutor monolayer. The scattering region was constructed by adding an extended region of metal electrodes to the ...
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Siesta: why are the transmission spectra affected by the bias voltage?
As I mentioned in my previous question siesta: current-voltage threshold value is not consistent with the band gap value,
at different bias voltages, we have different transmission spectra.
Why are ...
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Where are chemical potential windows [μR, μL] in the transmission spectra?
According to finite bias Non-Equilibrium Green’s Function (NEGF) method within the Landauer–Büttiker formula:
$$
I = \frac{2e}{h} \int_{-\infty}^{\infty} T(E) \left( f(E - \mu_L) - f(E - \mu_R) \right)...
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What happens to electronic structure of electrodes when we apply chemical potentials to them during NEGF calculations?
Assuming μL and μR are the chemical potential of left and right electrodes, and we are applying them to semiconductor electrodes. Assuming the chemical potential of one electrode is fixed,for example,...
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How to start a unrestricted hartree fock (UHF) calculation with a custom guess in PySCF?
At first I want to do a UHF calculation of Li$_2$ dimer with spin=6 which shall give a sequence of $\sigma_{1s} \sigma^*_{1s} \sigma_{2s} \pi_{2p_x} \pi_{2p_y} \pi_{2p_z}$ (ordering might be wrong) ...
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siesta: how many k points should be used in the TranSIESTA run in the transport direction?
I noticed the following words in the manual of siesta-5.0.0,
Note that k points should be limited in the TranSIESTA run, see
TS.kgrid.MonkhorstPack.
One should always use the same parameters in both ...
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sisl: is it possiple to extract band structure from external cells instead of created by sisl.geometry using Class sisl.physics.BandStructure
As for class sisl.physics.BandStructure(parent, point, division, name=None), could we make external cells into objects or array_like things which can be read by sisl.physics.BandStructure?
By the way,...
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siesta: how to determine the distance between metallic electrodes and channel materials at the interface?
We need attach the electrodes to channel materials (no matter the channel materials is 0D,1D ,2D or 3D),while we have to determine the distance between metallic ...
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siesta: which electrode is better when calculating seeback coefficient of a 2D semiconductor? bulk metal electrodes or semiconductor material itself
I would like to calculate the seeback coefficient of a 2D semiconductor.
I am thinking,
If I use bulk metallic electrodes, the semicondutor itself is not heated because transiesta can only put ...
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Siesta: Is that the advantage of using bulk-like metallic electrodes we can calculate channel materials of arbitrary length?
When we talk about adding extra screening layers to screen charges towards electrodes when we use semiconductors as electrodes,it sounds like the screening layers are not what we expect in our device. ...
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siesta: Are the results reliable if I use semiconductors as electrodes with long screening layers?
If I have enough computing resources to process very large systems so that I could use semiconductors as electrodes no matter how long the screening layer needed, will the results I get be reliable or ...
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siesta: Why are graphene nanoribbons with finite gaps used as electrodes without needing much more screening layers?
I did know one should use bulk-like metallic electrodes to avoid problems with screening and Fermi-level definition, and if I have to use semiconductors as electrodes, I need extra screening layers in ...
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siesta: Why is the current 0 for V < 0.8?
I met same problem in this questionsiesta: current-voltage threshold value is not consistent with the band gap value
After I finished this tutorial https://github.com/zerothi/ts-tbt-sisl-tutorial/tree/...
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siesta: current-voltage threshold value is not consistent with the band gap value
I am simulating the current-voltage characteristic of armchair graphene nanoribbons.
Here is my device:
First, I got the band structure of armchair graphene nanoribbons electrode in its supercell.
...
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Temperature dependent Structural and electronic Properties in Quantum espresso
I want to calculate temperature properties of hexagonal materials. Specifically, I want to know how lattice parameters, bond lengths and atomic positions changes. Further I want to compute thermal ...
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How to compute molar Gibbs free energy (chemical potential) for single molecule using gaussian09?
I want to calculate the Gibbs free energy of single gas molecule (AsH3) using Gaussian 09, but I am confused between "Thermal correction to Gibbs Free Energy" and "Sum of electronic and ...
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Are there non-antisymmetric solutions to the electronic Hamiltonian?
In electronic structure theory, one seeks solutions of the molecular electronic Hamiltonian
$$
H_e(\vec{R}) = T_n(\vec{r}) + V_{ne}(\vec{r};\vec{R}) + V_{ee}(\vec{r}) + const,
$$
where $\vec{r}$ are ...
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t2g-eg resolved PDOS analysis [duplicate]
I was attempting to analyze the t2g-eg resolved PDOS for transition metal-containing systems. Here, I have taken an example where three types of transition metals are present in octahedral geometry: $...
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Different results from MP2 calculations on same geometry in ORCA
I am trying to do a segmented potential energy scan around a dihedral for a molecule. I have optimized the geometry to a minima, and the scan runs from [-180, 180] in steps of two points at a time.
...
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what determines the 'Estimated total dynamical RAM ' in a Quantum Espresso calculation
As per my understandings the computer resources required for a DFT calculation increases by an order of three with the number of atoms.
But as you can see in the output files given below the ...
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In which irreducible representations shall I put the electrons in an F atom in PySCF?
I’m looking to complete ROHF energy calculations in PySCF for the F atom.
I need to update the irrep_nelec dictionary for F.
I know that the one for the O atom is:
...
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Applying Pressure in z-direction in quantum espresso
I am working with Bilayer 2H-MoS2, interlayer spacing ~3A. I want to apply pressure in z-direction which can lead to reduction in interlayer spacing, and then calculating its electronic properties. so,...
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How is the form of the active space electronic Hamiltonian derived?
The electronic Hamiltonian in the canonical orbital basis has the following form:
$$\tag{1}
H_e = h_0 + \sum_{ij=1}^{N} h_{ij} \sum_{\sigma \in \{\uparrow,\downarrow\}} a_{i\sigma}^\dagger a_{j\sigma} ...
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Why is my hydrogen energy not equal to -0.5 hartrees?
I'm trying to calculate the HOMO of various molecules in water solution. I first tried to see how PySCF calculates the HOMO of hydrogen. I ran the following code:
...
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488
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Why use PySCF/OpenMolcas instead of VASP/QuantumESPRESSO
While I am aware that VASP and QE are widely used for solid-state materials and PySCF/OpenMolcas are primarily designed for molecular systems.
I want to know why should I use PySCF/OpenMolcas for ...
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Materials with low band gap and low conductivity simultaneously. Is it possible?
I'm working on a data-driven project involving material properties and I'm wondering about the following:
I know that the notion of band gap and electrical conductivity are inversely related, and the ...
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'The combination of multiplicity electrons is impossible' in Gaussian
I am trying to calculate the energies of the S1 and T1 states of a molecule with UDFT using Gaussian.
For the T1 state, I can successfully use the following input file:
...
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How to Model Cations or Anions for Activation Energy Barrier Calculation in VASP for Electron Exchange Reactions?
I am interested in performing activation energy barrier calculations using VASP (Vienna Ab initio Simulation Package) specifically for reactions involving electron exchange. However, I am uncertain ...
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What are the parameters in PySCF's Selected Configuration Interaction code
Dear StackExchange Members,
I'm using the native PySCF implementation of selected configuration interaction (SCI). However, I can't seem to find any documentation detailing the algorithm or various ...
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How to use the CI method to compute the order of the molecular orbitals of the nitrogen molecule
It is well known that the Hartree–Fock (HF) approximation predicts a wrong order for the last two molecular orbitals of N$_{2}$. The calculations indicate that the 1$\pi_{u}$ orbital has higher energy ...
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How do I get the energy, if I have the wavefunction?
I recently wrote a simple HF SCF program for my understanding and realized that I do not fully understand such QM calculations.
Suppose I have the ground state gaussian wave function of a system,
$$
\...
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How did they calculate the indirect radiative recombination rate in this paper?
In this paper they calculated radiative recombination rates for Germanium using an effective mass model and I am trying to calculate the indirect spontaneous radiative recombination
rate related to ...
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How may I solve the radial Schrödinger equation?
I want to solve the radial Schrodinger equation for a Carbon atom with all six electrons.
The equation I want to solve is for $r>0$: $$[\frac{-\hbar^2}{2m}\frac{\partial^2}{\partial r^2}+ \frac{\...
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Spaces in Electronic band structure
I keep getting this whenever I try plotting the electronic band structure for CoRhMnGa on quantum Espresso, what could possibly cause the vertical spaces
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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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Why is electron correlation called the "chemical glue"?
A significant part of quantum chemistry involves developing methods that go beyond the Hartree-Fock theory which treats electron-electron interactions through a mean-field approach. From what I ...
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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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Reproduce Dissociation Energy of BH molecule with PySCF
I want to reproduce the bond dissociation energy of the BH molecule as stated in the book 'Molecular Electronic Structure Theory' by Helgaker et al, (chapter 8.3.1), using FCI with 1 frozen core ...
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445
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Quantifying relativistic effects in DFT calculations
I am wondering what is the best approach to quantify the contribution of relativistic corrections to a result of an electronic structure calculation. As far as I understand, from a user perspective ...
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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 is a relaxed reduced density matrix?
I am trying to understand how to calculate electronic properties using reduced density matrices from electronic structure calculation. So far, I understand (I think) that for the expectation value of ...
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How to obtain imaginary frequency polarizability?
I am trying to find a way to calculate $C_6$ dispersion coefficients for some atoms and molecules. In papers and textbooks, this quantity is introduced using the Casimir-Polder integral from the ...
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Computing proton-proton potentials for infinite periodic materials
For electronic structure calculation, when optimizing the wavefunction for an infinite periodic material, the proton-proton energy is needed to monitor the convergence of the SCF loop.
How is the ...
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How to get energy gap change at specific high symmetry points during ab initio molecular simulations？
I want to check the energy gap change during finite temperature ab initio molecular simulations. The results may look like this picture:
How can set aimd simulation to get this result in VASP?
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Plane wave expansion of the wavefunction for periodic material modelling
The aim is to do an electronic calculation with static nucleus with Plane wave (PW) basis functions for an infinite periodic material. The number of functions is given by the pairs of reciprocal ...
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Can the the relaxed energy of a material system (eV/atom) computed by DFT using VASP be positive?
If it is positive, why is it so? Is it due to specific convergence criteria or choice of pseudopotentials? I cannot check the convergence of the DFT calculations as they have been downloaded from a ...
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Plane-wave basis expansion for periodic material modelling: cutoff energy inequality and number of atoms in the simulation
The calculation of electronic structure of infinite periodic material using Plane-waves is the object of study here. The cutoff energy $E_{cutoff}$ provides information about the accuracy of the ...
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How to read UPF pseudopotential for ultrasoft pseudopotential simple in a fortran program
I'm currently working on calculating semiempirical local and nonlocal matrix elements for Ga. To proceed with my calculations, I need to extract specific parameters from the UPF (Unified ...
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What do we get by integrating over the charge density data of a material system calculated with DFT?
I am confused as to whether integrating over the charge density gets us the number of valence electrons in the material system or the total number of valence electrons in the material system.
Let's ...
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Unrestricted Hartree-Fock : Density matrices initialization
I have some results about the energy of H2 as a function of the bond length using Restricted HF (RHF) and Unrestricted HF (UHF) methods. With a zero-initialization of the density matrix I have the ...
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