Questions tagged [electronic-structure]
For questions concerning electronic structure concepts and calculations.
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What is the electrical behavior of the material with this band gap?
Presently I am doing DFT calculations to analyse the electronic structure of a material. I got the band structure as shown in the figure. I would like to know the electrical behavior of this material. ...
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0
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Calculating excited states using GAMESS CISD module [closed]
I am trying to compare the energies of the excited states of $\ce{C12H9N}$ molecule using the CIS and CISD module implemented in the quantum chemistry package in GAMESS.
While I can easily obtain the ...
6
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1
answer
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VASP error when trying to do calculations in the presence of an electric field
I am trying to observe the effect of the electric field on 2D materials. I applied electric field by introducing three tags:
...
12
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1
answer
650
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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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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 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 ...
- 2,363
16
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1
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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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Calculating single electron transfer [closed]
I'm thinking about doing some computational research about pyrazoline oxidation in chlorinated solvents under light. I've found plausible mechanism (article) that involves single electron transfer ...
- 2,363
9
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PT-symmetry leading to spin-degenerate band structures
I am trying to understand the fundamental physics of a kind of problem. I will introduce a specific example and then list some of the broader qualms I hold. I have observed many band structures, be it ...
- 2,342
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What differences are there when modeling metal-organic-frameworks as isolated clusters or periodic solids?
Should I take MOF (metal-organic framework) as a periodic structure or an isolated cluster? What's the difference between them? If it's periodic, can I do an analysis of the electronic structure, such ...
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How can I simulate the work function given by Ultraviolet Photoelectron Spectrum (UPS)?
How can I simulate the work function given by Ultraviolet Photoelectron Spectrum (UPS) of a molecule or a molecular crystal?
I thought it is an easy job: Just do a geometry optimization and get the ...
- 1,124
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How is the Bloch equation derived?
I am reading a textbook on many-electron theory, which gives a Bloch equation in its generalized form:
$$\tag{1}
[\Omega,H_0]P=Q(V\Omega-\Omega V_{eff})P,
$$
where $P$ denotes the projection from ...
- 3,813
11
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2
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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 ...
- 2,561
10
votes
2
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183
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Quantifying electronic overlap?
I am trying to understand how to quantify the electronic interaction/conduction/overlap between two metal cores at varying distances. As someone who works primarily with classical MD, and has less ...
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What is the physical meaning of occupations='smearing' in Quantum ESPRESSO?
I want to understand, what is the intuition behind using the occupations='smearing' or 'tetrahedra' in Quantum ESPRESSO input file? I mean how we can interpret what is going to happen inside of ...
- 2,561
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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 ...
- 2,561
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Why I get negative value of condensed Fukui functions?
Hello there,
I'm trying to calculate condensed Fukui functions for atoms of ascorbate (anion!). For some reason, when calculating nucleophilicity, the functions are negative. The equation I use is:
$$
...
user1247
9
votes
2
answers
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Incorporation of empty d-electrons of a p-block element in calculations in VASP?
Is it possible to incorporate the empty d-orbitals of a p-block element (suppose it is chlorine) into a VASP calculation?
If yes, what is the standard procedure to incorporate these orbitals.
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How to derive the k-path for monoclinic lattice structure?
Good afternoon all,
My post is inquiring about the mathematical derivation behind the Monoclinic crystal structure (c axis unique).
The Brillouin zone (BZ) I really would like to derive is shown below:...
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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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Is this G16 molecular hyperpolarizability error reproducible in other software?
I was trying to calculate the hyperpolarizability $\beta$ of a cluster of two water molecules in Gaussian16 using the route card:
...
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7
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Support for orbital-space Quantum Monte Carlo in CASINO?
Is CASINO code capable of performing orbital-space QMC calculations?
16
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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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Work Function Problem
2D materials (such as graphene) are mostly exfoliated from their 3D bulk counterpart. I am wondering how we can calculate work function for a 2D material? Normally electrostatic potential in the out-...
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Interpretation of electronic band structure diagram
I want to understand the electronic band structure diagram of the following image, corresponding to $\text{MoS}_2$ (TMD):
I read about DFT (density functional theory).
DFT is based on solving the ...
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answer
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Approach for Higher Order Response Properties
There are three (at least that I'm aware of) commonly used approaches to obtain linear response properties (e.g electric polarizability, optical rotation, NMR shielding tensors)
Sum over states: The ...
- 15.2k
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For which materials is the Bethe lattice a good model to compute the density of states of the conduction band? [closed]
The Bethe lattice is exactly solvable in the limit where each lattice site has an infinite number of nearest-neighbors. In this limit it yields a semi-circular density of states in the conduction band....
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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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How do the various programs read or write integrals in FCIDUMP format?
The FCIDUMP format was created by Peter Knowles and Nick Handy circa 1989 and now allows many electronic structure software packages to interact with each other.
...
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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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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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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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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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Conductivity Computations of Molecular Wires [closed]
I am interested to compute the conductivity properties of some molecular organic wires in SIESTA.
Since I am new in SIESTA, I would appreciate a guide for beginners to this field.
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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 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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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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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 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 "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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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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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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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 ...
- 15.2k
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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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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 ...
- 3,813
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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 ...
- 2,671
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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 ...
- 15.2k
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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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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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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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