Questions tagged [electronic-structure]
For questions concerning electronic structure concepts and calculations.
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Why does orbital-free DFT scale linearly with system size?
In answering another question here (Is there any relevant DFT formalism apart from the Kohn-Sham approach?), I came across numerous statements that Orbital-Free DFT should scale linearly with system ...
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How to determine, a priori, whether a compound has multireference character?
We say a system has multireference character if it is not well described at the SCF level by a single configuration/Slater determinant. Not accounting for this can lead to errors in post-SCF methods, ...
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What are the "smart algorithms" applied to solve the "curse of dimensionality"?
The "curse of dimensionality" is an ubiquitous issue arising in both electronic structure and quantum molecular dynamics, which refers to the exponential scaling of computational cost with ...
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How to overcome the exponential wall encountered in full configurational interaction methods?
Similar to how a molecular orbital, also known as a 1-electron wavefunction, can be represented with a linear combination of “basis” functions, e.g., atomic orbitals (LCAO):
$$\Phi(\mathbf{r})=\sum_i^...
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When do relativistic effects need to be explicitly included?
For many applications with heavy metals, pseudopotentials can be used to include some amount of relativistic effects. But for what sort of systems does it become necessary to actually use a ...
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Derivation of Slater-Koster equations
I am trying to derive the Slater-Koster equations (Table. 1 of Ref. 1) for the two-centre approximation of hopping integrals between atomic orbitals. I understand that Slater-Koster approximates the ...
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How can quantum computing accelerate materials modeling?
Materials modeling is very computationally intensive and first-principles simulation of a real system of reasonable size typically involves the use of classical supercomputers.
How can quantum ...
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What is the largest system that has been studied by the coupled cluster method?
This is parallel to the analogous question about the largest DFT calculation: What is the largest material that has been studied using density functional theory?
I assume we allow high performance ...
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How to incorporate the effect of spin-orbit coupling in electronic structure calculation
Since the effect of spin-orbit coupling plays an important role in many transition metal complexes, what are the common methods to incorporate the effect of spin-orbit coupling?
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How is group theory used to deduce which of these integrals are equal to 0?
The number of all two-electron integrals:
$$
\tag{1}
\langle \phi_1 \phi_2|\phi_3\phi_4 \rangle = \int d^3\mathbf r' \int d^3\mathbf r'' \, \phi_1(\mathbf r'') \, \phi_2(\mathbf r') \frac{1}{|\mathbf ...
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Is there a software that can do derivatives with respect to user defined vibrational modes?
I'm doing some property calculations that depend on a sum of derivatives of some quantity with respect to normal vibrational modes. I was hoping to find some physical intuition relating the type of ...
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Can DFT be considered an ab initio method?
Note added afterwards: This question also has excellent answers on the Chemistry Stack Exchange: Is density functional theory an ab initio method?
I have very little experience with DFT, but coming ...
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How to identify a semi-metal from the band structure?
Wikipedia says
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band.
How small/unique the overlap should be so that we can ...
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What approaches are employed to treat amorphous materials?
A lot of materials electronic structure research focuses on periodic structures like polymers, nanotubes/sheets, Metal Organic Frameworks (MOFs) and crystals, which makes them amenable to PBC ...
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What are some codes available for Dynamical Mean Field Theory (DMFT)?
One particularly field of matter modeling is that of strongly correlated materials, heavy-fermion compounds with partially filled 4f or 5f orbitals. In brief, these are materials whose complex ...
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Methods for visualising aromaticity
I was wondering what tools there are for visualising aromaticity and anti-aromaticity in molecules, to what quantum chemistry programs they are interfaced, and what other relevant features they have.
...
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Properties that can be deduced from Band structure and DOS
Calculation of band structure and Density of States (DOS) is ubiquitous in matter modelling research publications.
What are some properties that can be deduced from a band structure plot and density ...
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When should geometry relaxation not be performed?
My understanding is that geometry relaxation (i.e. letting the nuclei follow the force gradients of the PES until they reach local minima) should usually be performed in order to get the correct ...
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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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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 ...
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Total spin and/or multiplicity for transition metal ions?
I am trying to input various charge states of various transition metal ion species into DFT calculations. The program requires an input of multiplicity = 2*(total spin) + 1.
I have an undergraduate-...
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What is the largest system for which vibrationally resolved electronic spectra have been simulated using ML-MCTDH?
Multi-layer Multi-configuration time-dependent Hartree (ML-MCTDH) is a method widely used for simulation of vibrationally resolved electronic spectra that incorporate the coupling between vibrational ...
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Is Heisenberg model or in its simplier form Ising model a good approximation to study magnetic systems?
Heisenberg model
$$\hat{H}=-\sum_{\langle i j\rangle}J\hat{S}_i\hat{S}_j$$
And in its simplified version, the Ising model
$$\hat{H}=-\sum_{\langle ij\rangle}J\hat{S}_i^z\hat{S}_j^z$$
are widely ...
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How to calculate energy of a molecule in an aligned electric field?
So I am aware that many quantum chemical codes are able to add external fields to molecular calculations (for example to calculate polarizabilities). I also know that in some (eg. Orca) you have some ...
user430
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What are the computational limits of explicitly correlated methods?
Expanding the $N$-electron wavefunction in terms of Slater determinants (as in CI and CC theory) could lead to a very slow convergence to its basis set limit because such expansions can't give an ...
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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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Approximation of Dyson's Equation
I've been trying to learn about Green's function in the context of computational chemistry by reading Szabo and Ostlund's Modern Quantum Chemistry.
I've reached a section about the one particle many ...
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How to model phase transitions at critical regions in a magnetic system?
Is there any first principle method available to study phase transitions at the critical region for ferromagnetism (FM) or antiferromagnetism (AFM)?
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How to convert Unified Pseudopotential Format (UPF) into Ultrasoft Pseudopotential (USPP) format?
I am working on DFT code having plane wave along xy axis and bspline in z direction. For calculating the properties of TMD materials, spin orbit coupling must be included but i did not find fully ...
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What is a good practical way to determine whether or not I need to use a multiconfigurational method?
I’m planning to run a calculation of single electron transfer where my system goes from singlet to triplet biradical (presumably). So I’m wondering how to decide if I need to use milticonfigurational ...
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How to make heterostructure/heterojunction structure?
How can I make a heterostructure or a heterojunction of ZnO/MgZnO for optimization with WIEN2k code?
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For DFT and Hartree-Fock, how can we know that we have a true minimum? Is there an equivalent to the "frequency analysis" for geometry optimization?
In a geometry optimisation, one can check if they have reached a minimum by checking the phonons. And to a certain extent, the global minimum can be confirmed by relaxing from different starting ...
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What is the mathematical condition that ensure that the self-consistent field (SCF) procedure must converge?
We know that there is convergence issue of DFT method on study real molecular system. It would be conducive if people could pre-determine if the SCF procedure is converge analytically before starting ...
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What do the rows and columns of a Fock matrix represent?
I am using the pyscf code, where the Fock matrix can be obtained by:
...
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Increasing k-point grid to take DOS calculation
I was trying to compute some electronic properties for Pd using SIESTA and VASP for some computer practicals in my university, specially focused on band structure and density of states (DOS) using LDA ...
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What are some of the advantages and disadvantages when using shape consistent pseudopotentials as compared to energy consistent pseduopotentials
From the literature as well as the answer to the question What is the meaning of energy-consistent and shape-consistent in the context of pseudopotentials? I can see that the key difference between ...
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What are the practical limitations of R12/F12 methods?
Electron correlation methods based on an expansion of the $N$-electron wavefunction in terms of Slater determinants have a slow basis set convergence. Moreover, explicitly correlated methods (such as ...
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Comparing GAMESS, OpenMOLCAS and Psi4
Over the years many open-source ab initio packages have been developed and the diversity in subroutines, methods and portability (ability to interface with other software) is quite varied for ...
user784
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Avoiding charge-migration in electronic structure calculations with solvent-like environments
When performing electronic structure calculations on a molecule, one can surround it with point charges to mimic a solvent environment, and lend polarization effects. There is a bit of a caveat ...
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How does one project out the translations and rotations from a Hessian?
I've recently written a simple code to numerically compute the Hessian of some function (at a point). Most electronic structure packages will compute the Hessian and then project out the translations ...
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How may I calculate the "effective transfer integral" in free electronic-structure software? [closed]
I would like to calculate the following four quantities in a free electronic structure program:
\begin{alignat}{2}\tag{1}
e_1&=\langle\phi_1|H^{KS}|\phi_1\rangle,\\
e_2&=\langle\phi_2|H^{KS}|\...
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Is there an energy gap correction factor that needs to be used in DFT calculations?
I am a beginner and have performed the DFT calculation in Quantum ESPRESSO for calculation of the direct and indirect bandgap of Silicon. I found the indirect bandgap to be 0.6551 eV. Now, I have ...
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Why is it so hard to find the ground state of molecules with d-block or f-block elements?
Based on some of my previous reading and questions that I have asked I am aware that determining the ground state electronic configuration for molecules containing d-block elements theoretically is ...
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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
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Plotting density of states of Fe(BCC) using Quantum ESPRESSO
I have run the DFT calculation and plotted DOS of Fe(BCC) in Quantum ESPRESSO. I have attached the plot:
(click on image to see clearly)
But It's a wrong plot as it is not matched with the referenced ...
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How can I find the parameters in a basis set?
I have a question about the basis functions of Gaussian. When the basis function is set (e.g., 6-31G), I would like to know the specific value of Gaussian's parameters for each atom.
In particular, I ...
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Codes for post-processing Gaussian cube files?
I have generated MOs of a molecular system and I need to recreate its electronic density via $\rho(r)=\sum_{A_i}|\psi_i(\mathbf{r})|^2$ where $A$ is a set of occupied MOs. I am trying to do this via ...
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Visualize electron density using pyscf
I found the following example of code which uses density functional theory to compute the electron density $\rho$:
...
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How can I be sure that I have found the conduction band minimum in DFT?
Let's say I want to find the electronic energy bands from DFT calculations in VASP along a chosen path in the Brillouin zone.
Now, I want to make sure I choose a path that captures the conduction band ...
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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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