Questions tagged [electronic-structure]

For questions concerning electronic structure concepts and calculations.

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3
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1answer
20 views

Question regarding conflicting results of checking the electron-preciseness of isoelectronic species via NBO and EHM calculations

(Cross-posting from Chemistry.SE due to recommendation that this be posted here; see comment section) It is well known that the tert-butyl cation's empty 2p orbital on the central carbon is stabilised ...
12
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1answer
224 views

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 ...
10
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2answers
175 views

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 ...
7
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1answer
83 views

Electron interactions between different positions or different orbitals

When I consider the grid positions $r$ in a molecular system, I have a matrix, where each row can be regarded as an N-dimensional vector and each column can be regarded as a G-dimensional vector. In ...
5
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1answer
132 views

Ground State energy trick for many-body electronic structure calculations?

I am an outsider to this field, so I am not sure about the validity of my work below. Let us define the following Hamiltonian from DFT: $$ \tag{1}H_{ij} \psi_{ij} \equiv (-\frac{\hbar^2 \nabla_i^2}{2m}...
11
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3answers
674 views

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 ...
6
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0answers
50 views

Orbital space clustering

I am interested in how the orbital space of a system can be partitioned into clusters. I read reading 'Cluster many-body expansion: A many-body expansion of the electron correlation energy about a ...
5
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0answers
54 views

How to calculate energy gradient and Hessian with respect to only a few internal coordinates using Gaussian?

I would like to form the (numerical) gradient and the Hessian of the total electronic energy with respect only to a few internal coordinates (namely, the six intermolecular coordinates of a weakly ...
6
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2answers
159 views

How to find out the multiplicities of molecules containing d and f block species?

I know that the U atom has four unpaired electrons. Therefore it has a total spin S of 2. This means its multiplicity is 2S+1 = 5. Now consider a complicated molecule such as $UF_6$. In theory all I ...
12
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2answers
305 views

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 ...
4
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0answers
41 views

DFT Vasp calculation not converging when doing a SCF calculation for monolayer MoS2 [closed]

I am trying to calculate the electronic structure of Monolayer Molybdenum Disulfide ($\ce{MoS_2}$) using Vasp. However, I encounter problems with convergence. It does not seem that my calculations ...
8
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2answers
57 views

Are there efficient open source implementations of electrostatic potential integrals?

We've had several questions regarding calculation and plotting of electron density. The electrostatic potential represents the interaction between a point charge at a given point $\mathbf{r}$ in a ...
7
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1answer
96 views

Visualize electron density using pyscf

I found the following example of code which uses density functional theory to compute the electron density $\rho$: ...
8
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2answers
108 views

Can the color of gold metal be reproduced by modeling only the conduction electron band structure, or do atomic absorption lines contribute?

@JohnCuster's answer to Why is gold golden? is based on the band structure of the delocalized conduction electrons in gold, whereas other answers there tend to support the "Gold is gold due to ...
7
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1answer
90 views

Computing analytic derivatives of molecular Hamiltonians obtained from solving Hartree-Fock equations

I'm currently working on a quantum chemistry project, I am dealing with a second-quantized electronic Hamiltonian (corresponding to some molecule), written in terms of fermionic creation and ...
5
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1answer
94 views

Calculating first and second derivatives of a molecular Hamiltonian?

I'm interested in computing first and second derivatives of molecular Hamiltonians with respect to nuclear coordinates. I've been using Psi4 and PySCF to perform Hartree-Fock calculations, and I was ...
8
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0answers
106 views

Error while doing a band structure calculation in Quantum ESPRESSO

I have been using BURAI GUI of Quantum ESPRESSO to calculate the optical properties of ZnSe quantum dots. But first I wanted to calculate the electronic band structure. After running the calculation ...
10
votes
1answer
226 views

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 ...
9
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1answer
150 views

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. ...
6
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0answers
75 views

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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1answer
211 views

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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1answer
160 views

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 ...
12
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2answers
75 views

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 ...
13
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1answer
106 views

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 ...
14
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1answer
337 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 ...
9
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1answer
166 views

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 ...
7
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1answer
105 views

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 ...
9
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1answer
70 views

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 ...
8
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1answer
140 views

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 ...
10
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2answers
692 views

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 ...
10
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2answers
83 views

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 ...
8
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1answer
1k views

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 ...
11
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2answers
876 views

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 ...
7
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1answer
164 views

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: $$ ...
9
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2answers
122 views

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.
9
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1answer
328 views

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:...
10
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4answers
753 views

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 ...
8
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1answer
142 views

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: ...
7
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1answer
86 views

Support for orbital-space Quantum Monte Carlo in CASINO?

Is CASINO code capable of performing orbital-space QMC calculations?
15
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2answers
280 views

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 ...
7
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1answer
90 views

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-...
3
votes
1answer
83 views

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 ...
8
votes
1answer
34 views

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 ...
8
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0answers
55 views

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....
19
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4answers
374 views

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 ...
8
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1answer
146 views

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. ...
15
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3answers
351 views

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 ...
21
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2answers
443 views

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 ...
12
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2answers
617 views

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: ...
11
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2answers
304 views

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 ...