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Questions tagged [electronic-structure]

For questions concerning electronic structure concepts and calculations.

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3 votes
1 answer
52 views

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 ...
3 votes
0 answers
41 views

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 ...
12 votes
4 answers
998 views

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 ...
4 votes
0 answers
85 views

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: $...
8 votes
3 answers
240 views

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. ...
3 votes
1 answer
109 views

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 ...
0 votes
1 answer
47 views

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: ...
1 vote
0 answers
28 views

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,...
5 votes
1 answer
44 views

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 ...
3 votes
1 answer
64 views

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} ...
15 votes
2 answers
2k views

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: ...
23 votes
3 answers
810 views

What is the largest system that has been studied by the coupled cluster method?

This is parallel to the analogous question about the largest DFT calculation: What is the largest material that has been studied using density functional theory? I assume we allow high performance ...
7 votes
1 answer
430 views

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 ...
6 votes
0 answers
69 views

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 ...
7 votes
1 answer
274 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 ...
2 votes
1 answer
448 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: ...
1 vote
1 answer
97 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 ...
6 votes
2 answers
189 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, $$ \...
6 votes
2 answers
399 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{\...
3 votes
0 answers
77 views

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 ...
7 votes
2 answers
173 views

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 ...
0 votes
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
17 votes
1 answer
3k views

Gaussian-type orbitals vs Slater-type orbitals in terms of computational efficiency

When creating molecular orbitals via the linear combination of atomic orbitals method I am told that Slater orbitals provide a more accurate representation whilst Gaussian orbitals are computationally ...
2 votes
0 answers
63 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 ...
7 votes
1 answer
586 views

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 ...
3 votes
0 answers
50 views

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 ...
9 votes
2 answers
423 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 ...
2 votes
0 answers
20 views

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 ...
3 votes
0 answers
66 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 ...
6 votes
1 answer
102 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 ...
5 votes
1 answer
83 views

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 ...
3 votes
1 answer
77 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 ...
4 votes
1 answer
136 views

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 ...
4 votes
1 answer
158 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 ...
3 votes
0 answers
26 views

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?
2 votes
1 answer
52 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 ...
4 votes
2 answers
314 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 ...
5 votes
3 answers
305 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: ...
5 votes
1 answer
159 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 ...
4 votes
1 answer
115 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 ...
6 votes
1 answer
146 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.
5 votes
1 answer
309 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 ...
3 votes
1 answer
260 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 ...
2 votes
1 answer
160 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: ...
5 votes
1 answer
558 views

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, ...
6 votes
1 answer
384 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 ...
6 votes
0 answers
63 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 ...
5 votes
1 answer
343 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?
2 votes
0 answers
48 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 ...
2 votes
0 answers
89 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 ...