Questions tagged [electronic-structure]
For questions concerning electronic structure concepts and calculations.
149
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What are alpha and beta electrons?
Question
The mwfn filetype includes fields for alpha and beta electrons/orbitals/density matrices.
What is the definition of alpha and beta electrons; what distinguishes them?
For future research, ...
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Which is better for binding energies: DFT-D3 or RI-MP2?
I am trying to calculate the binding energy of a small molecule with an underlying surface. I have used B3LYP-D3BJ (as implemented in ORCA) at def2-TZVP basis set to optimize the geometry of the VdW ...
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Benchmarking DFT vs Experimental Gaps - Confusion over Fundamental and Optical Gaps
Recently, I've come across discussions about the differences between fundamental (or electronic) bandgaps and optical bandgaps, with the two quantities differing mainly by the electron-hole binding ...
- 1,014
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Python library to obtain atomic orbitals of atoms in the lowest energy state
I want to code an UHF code. Hence for each atom I need the lowest energy electronic configuration. Is there a python package/library that already does it?
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PySCF two-electron integrals between two fragments
I am trying to compute integrals of the form $(pq|rs)$ where the orbitals $p$ and $q$ are orthogonalized atomic orbitals for a fragment $A$ and $r,s$ are orthogonalized on fragment $B$. I was thinking ...
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Variation of Conduction band minimum and valence band maximum with applied strain in semconductors
I have been using the Deformation Potential theory to evaluate the electron scattering rates in nanomaterials. In each case, I was under the impression that the Conduction Band Minimum (CBM) and the ...
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Determination of fluorescence lifetime by using oscillator strength?
$$k_r=2.88\times10^{-9}n^2\langle\tilde{v}\rangle_\text{av}^2 \int\varepsilon_{\tilde{v}}d\tilde{v}$$
$$f=4.32\times10^{-9}\int\varepsilon_{\tilde{v}}d\tilde{v}$$
I plan to use the above equations to ...
- 21
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Inconsistent band structure of bilayer graphene
Context
I am performing band structure calculations for bilayer graphene using QE codes. I used X-crysden for the k-point mesh ...
- 31
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Graphene Band Structure with SIESTA
I am struggling with getting a correct band structure for even pristine graphene using SIESTA. The issue is almost certainly the K point path. My graphene sheet (128C atoms) isn't the traditional ...
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Electronic Structure Calculation with External Field
There are various programs for calculating energy states for molecules (ORCA, Gaussian, ...). Is there also software that allows the same simulations with an additional external potential (e.g. ...
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DFT calculation for conjugated polymers
I am new to DFT calculation.
I want to know the structure of conjugated polymers (plane angle, etc.) and their electronic and optical properties (such as HOMO-LUMO, IR, etc.).
I am using 6-311+G(d) ...
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How to perform carrier doping (hole/electron) for 2D materials by Quantum Espresso?
I tried to set the tot_charge parameter of Quantum Espresso to alter the charge of the system, but the phonon spectrum I obtained was very strange. Could anyone ...
- 31
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Electronic structure of s-indacene
Structure shown in (a) is the regular $s$-indacene molecule, and (b) is a structure that i generated such that the central six-member ring remains similar to benzene. It is well-known in literature ...
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Modelling 2D semiconductor heterostructures including one magnetic layer with QE
I want to compute the electronic structure of a heterostructure composed of two 2D monolayers. I am stacking a TMD monolayer on top of a magnetic 2D monolayer. Both of them are semiconductors.
Do I ...
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What is the difference, if any, between an effective core potential (ECP) and a pseudopotential?
I've used these terms interchangeably for a while, but have noticed that in PySCF they are separate attributes.
Are there any crucial differences between an effective core potential (ECP) and a ...
- 219
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pyscf - non-orthogonal CI
I'm kinda new to pyscf and was wondering if there is a way to implement non-orthogonal CI calculations with it. I would appreciate any help.
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Would it be appropriate to use a Van der Waals-DFT approximation in Quantum ESPRESSO to study the properties of my material (p-type semiconductor)?
I want to study the structural, optical, electronic and transport properties of my material that contains Cu atoms using Quantum ESPRESSO. I tried so many approximations but every time I face an issue ...
- 1,785
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Why do I get very intense picks when I use PBE0 with NC PP?
I used PBE0 to get projected density of states using norm-conserving pseudopotentials with Quantum ESPRESSO. I found very intense picks (scf -> projwfc ) compared to the ones that I found using ...
- 1,785
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How to add the scissor operator in Quantum ESPRESSO input?
I want to calculate the optical, transport and electronic properties of my material. GGA underestimate the bandgap.
I tried GGA+U but the bandgap is still underestimated and also when I tried to use ...
- 1,785
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Issue with getting pw_bands output file for ws2
After running the input pw_bands.in file execution is not stopping even after 10hrs , and the output is not updating anything further after 1 min of the output.
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NBO analysis of potentially hypervalent compounds
I know that one can determine which type of bond is present between different atoms in a molecule by analyzing the output of an NBO analysis. Furthermore the second order perturbation theory analysis ...
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What makes the inhomogeneous electron gas more interesting than its homogeneous counterpart?
This question is asked in the context of the famous paper on DFT by Hohenberg and Kohn. What makes the inhomogeneous electron gas more interesting than its homogeneous counterpart?
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Understanding derivation of geminal based methods [closed]
Cross-posted on Reddit.
I have been reading through [1] to get a better understanding of geminal based methods. This is one of two questions that I'm asking about that paper on this site, the other ...
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Optical Band gap determination from absorption coeffecient using DFT
I am currently working with a perovskite material which shows forbidden transitions. Older studies used bigger values of $\alpha$ in HSE06 calcualtions(to match with experimental Band Gap) but a ...
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How is the zero energy defined for molecular orbitals?
In DFT and Hartree-Fock bonding orbitals have negative energies while antibonding orbitals have positive energies. Why is this the case? It seems this is due to the zero-point energy being defined for ...
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Should one perform geometry optimisation before calculating electronic/phonon band structures via DFT?
I am new to DFT calculations and I would like to get the electronic and phonon band structures of FeSn (1 kagome layer and 1 Sn layer in between). My question is, is it absolutely necessary to first ...
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Are frozen-core approximations for the elements of first or second row accurate for potentially extremely short bond distances present in the molecule
Yes, it is about my molecule that you've heard of (but never seen) in my previous questions. The molecule, which contains only C, Al, B, Cl, Mg, N, O, S and Si, is macromolecular with quite crowded ...
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Does the RI method actually accelerate basis convergence of MP2, "by one more zeta"?
It is often said that the resolution of the identity (RI) method accelerates the basis set convergence rate of MP2 "by one more zeta", e.g. that RI-MP2/cc-pVTZ/cc-pVTZ results are close to ...
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How can I get the projected density of states within the Green's function method?
I have this Green's function matrix $G^r= (E \mathbb{I} - \hat{H})^{-1}$ in the $|\textrm{site}\rangle\otimes|\textrm{orbital}\rangle\otimes|\textrm{spin}\rangle$ Hilbert space, and I am curious if ...
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Zig zag straight lines bands from Quantum Espresso calculations [closed]
During band structure calculations in Quantum espresso I found that the bands are coming in Linear form and not curvature. Why is this happening? Is there any explanation for this? Which parameters ...
- 1,095
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616
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How to detect an "open shell" molecule?
I feel like this is a really stupid question, and I've been ashamed to ask for a while...
When I'm about to run some electronic structure calculation on a molecule, how do I know if I need to use an ...
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Is the Grand Unified Theory of Classical Physics (GUTCP) valid/accurate for atoms and molecules?
The Grand Unified Theory of Classical Physics (GUTCP) is sort of a non-mainstream theory proposed by Mills, https://brilliantlightpower.com/book-download-and-streaming/
Looks like the books showed ...
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Need help about how I can get/generate semicore pseudopotentials to be used in Quantum Espresso DFT?
I would like to know if I can get/generate semicore pseudopotentials (some core electrons are also considered along with valence electrons) to be used in Quantum Espresso DFT. Actually, it would be ...
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Do bonds between the atoms influence ab-initio energies?
As you know, oxygen has two available states. However, the picture above illustrates oxygen (red) has a just one bonding with one carbon. I am kind of afraid it makes differences compared that an ...
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What are the limitations of FCI?
I am aware of the fact that Full Configuration Interaction scales poorly. Taking into account that the number of $n$-times excited Slater determinants of an $N$-particle System with $M$ basis ...
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Cause of segfault from simple Gaussian16 input?
First of all, I already did electronic structure calculations in the past, but I am a total beginner regarding the use of Gaussian. Currently I am trying to use Gaussian16 through the terminal on ...
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Electric field calculations VASP [closed]
Does anybody have experience in electric field calculations using VASP? I gave the electric field to an already relaxed structure and it shows ...
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Understand the energy level of "oxygen hole" created by substitutional Al doping in TiO2 [closed]
By substituting a Ti atom in anatase $\text{TiO}_2$ lattice with a Al atom, an oxygen hole $\text{O}^-$ will be created considering a formal charge of +4 for Ti, -2 for O and +3 for Al .
In this paper ...
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Have experimental electron densities ever been used in a DFT calculation?
I know it is possible to measure electron densities from certain types of scattering experiments.
Have these densities ever been fed into density functionals to calculate energies and other properties?...
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Attempts to define atomic energies based on electron density?
The concept of an atom in a molecule is undefined in quantum mechanics. Consequently, very useful properties like atomic charges, bond orders, and so on cannot be rigorously defined. There are many ...
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Meaning of Kronecker Product in Transport Theory behind BoltzTrap2
I am somewhat confused by the use of a Kronecker Product in Madsen, Georg K. H. et al. “BoltzTraP2, a program for interpolating band structures and calculating semi-classical transport coefficients.” ...
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Are multiplet free atoms multireference?
In general, my understanding is that free radicals and non-equilibrium molecules sometimes need multireference electronic structure calculations, mainly because of different electronic states being ...
user5418
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Textbooks for electronic structure theory
Through this post I am looking to create a resourceful list of textbooks for any one interested in electronic structure theory.
The focus here is to create mostly a mutually exclusive list of answers ...
user784
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electronic structure of (110) Nb [closed]
I need to get the optimal number of layers of (110) niobium that is a good representative of the behavior of the material, but I am facing two problems using Quantum Espresso,
I Keep getting the ...
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Fitting GTOs to other density/wavefunction representations - state of the art?
When using most molecular electron structure codes that use GTOs for the density or wavefunction, it is possible to project the first-order density matrix onto 'natural orbitals' with MOs expressed ...
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2
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FCI without Hartree-Fock
Recently, I came across some lecture notes on electronic structure theory which had something peculiar about it. I noticed that FCI (configuration interaction) was introduced before Hartree-Fock ...
user784
9
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2
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Numerically integrating the Hartree potential
I'm trying to write a 1D density functional theory code on Python to predict the electronic structure of certain ions using the local density approximation.
I'm trying to construct the hamiltonian for ...
6
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Is it possible to calculate the dipole polarizability in the presence of a nonzero electric field?
One common way of calculating a dipole polarizability from electronic structure is by calculating the following derivative by finite difference:
$$
\mathbf{\mu}=\left(\frac{\partial U}{\partial \...
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Cheap NMR shift calculations in periodic systems
I am looking for an electronic structure method code (e.g. tight binding DFTB) that supports cheap calculations of NMR shieldings and has support for periodical systems. I would be grateful for any ...
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Do the U values affect structure optimization with the DFT+U simulation to optimize crystal structure?
I am trying to do structure optimization of TiO2, since titanium is a transition metal, I need to use DFT+U to simulate the right band structure, but the electronic band structure would also affect ...
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