Questions tagged [electronic-structure]

For questions concerning electronic structure concepts and calculations.

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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 ...
Jaafar Mehrez's user avatar
6 votes
1 answer
252 views

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 ...
James Arten's user avatar
2 votes
1 answer
54 views

'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: ...
Laura's user avatar
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4 votes
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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 ...
Nidhi Tiwari's user avatar
6 votes
0 answers
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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 ...
AWPrentice's user avatar
1 vote
1 answer
74 views

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 ...
AlfredV's user avatar
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140 views

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, $$ \...
ipcamit's user avatar
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3 votes
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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 ...
Peter Pien's user avatar
6 votes
2 answers
393 views

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{\...
L Maxime's user avatar
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0 answers
30 views

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
Jeremiah Okotie's user avatar
2 votes
0 answers
56 views

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 ...
Prasad's user avatar
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7 votes
2 answers
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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 ...
Fracton's user avatar
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1 answer
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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 ...
Mikke Mus's user avatar
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3 votes
0 answers
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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 ...
jakg's user avatar
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9 votes
2 answers
377 views

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 ...
Szgoger's user avatar
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2 votes
0 answers
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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 ...
Juandiego Velasquez Benites's user avatar
3 votes
0 answers
35 views

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 ...
Szgoger's user avatar
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5 votes
1 answer
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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 ...
Szgoger's user avatar
  • 624
4 votes
1 answer
157 views

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 ...
mle's user avatar
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3 votes
0 answers
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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?
Tieyuan Bian's user avatar
3 votes
1 answer
68 views

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 ...
mle's user avatar
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4 votes
2 answers
259 views

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 ...
Pranoy Ray's user avatar
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2 votes
1 answer
48 views

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 ...
mle's user avatar
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4 votes
1 answer
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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 ...
Raj Kumar Paudel's user avatar
5 votes
1 answer
118 views

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 ...
Pranoy Ray's user avatar
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4 votes
1 answer
91 views

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 ...
mle's user avatar
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5 votes
1 answer
150 views

Contents of a CHGCAR file and how to read it appropriately in Python? [duplicate]

Rephrasing the above, what is the content of the data in the CHGCAR file? Is the data part shown below representative of the electron-charge density or is it the actual charge in the system and I have ...
Pranoy Ray's user avatar
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2 votes
1 answer
97 views

ORCA Error: NCalcs not set

I've been getting the following error whenever I use CCSD(T) and the ORCA Forums don't have an answer to this one: ...
znc204's user avatar
  • 63
5 votes
3 answers
163 views

How do I obtain CB and VB values from Quantum ESPRESSO?

Can someone explain to me please how am I supposed to get this: From this: I'm a little bit confused because in my calculations using Quantum ESPRESSO I found that: ...
Camilla's user avatar
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5 votes
1 answer
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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, ...
Adam's user avatar
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6 votes
1 answer
313 views

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 ...
Hemanth Haridas's user avatar
5 votes
0 answers
44 views

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 ...
CW Tan's user avatar
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5 votes
1 answer
335 views

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?
mle's user avatar
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2 votes
0 answers
34 views

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 ...
Szgoger's user avatar
  • 624
6 votes
1 answer
87 views

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 ...
PBH's user avatar
  • 2,653
2 votes
0 answers
76 views

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 ...
Yasir Ulutas's user avatar
3 votes
0 answers
94 views

Inconsistent band structure of bilayer graphene [closed]

Context I am performing band structure calculations for bilayer graphene using QE codes. I used X-crysden for the k-point mesh ...
Akash Saxena's user avatar
2 votes
0 answers
161 views

Graphene Band Structure with SIESTA [closed]

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 ...
Elie H's user avatar
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3 votes
0 answers
145 views

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. ...
Johny Dow's user avatar
5 votes
1 answer
157 views

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) ...
Duy-Minh Hoang's user avatar
3 votes
0 answers
168 views

How to perform carrier doping (hole/electron) for 2D materials by Quantum Espresso? [closed]

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 ...
zt liu's user avatar
  • 31
4 votes
1 answer
63 views

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 ...
Hemanth Haridas's user avatar
4 votes
1 answer
59 views

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 ...
franz's user avatar
  • 297
3 votes
1 answer
276 views

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 ...
jjgoings's user avatar
  • 221
6 votes
1 answer
127 views

Has non-orthogonal CI (NOCI) been implemented in PySCF?

I'm kinda new to Pyscf and was wondering if there is a way to do non-orthogonal CI calculations with it. I would appreciate any help.
master_disaster's user avatar
3 votes
1 answer
199 views

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 ...
Camilla's user avatar
  • 2,049
3 votes
0 answers
47 views

Why do I get very intense picks when I use PBE0 with NC PP? [closed]

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 ...
Camilla's user avatar
  • 2,049
3 votes
1 answer
192 views

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 ...
Camilla's user avatar
  • 2,049
3 votes
0 answers
30 views

Issue with getting pw_bands output file for ws2 [closed]

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.
PAWAN KUMAR's user avatar
6 votes
2 answers
112 views

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 ...
C_Swann22's user avatar
  • 573