Questions tagged [electronic-structure]

For questions concerning electronic structure concepts and calculations.

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9
votes
2answers
56 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 ...
7
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0answers
59 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
votes
2answers
785 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
votes
1answer
120 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
votes
2answers
92 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
votes
1answer
126 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
votes
3answers
342 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
votes
1answer
99 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
votes
1answer
82 views

Support for orbital-space Quantum Monte Carlo in CASINO?

Is CASINO code capable of performing orbital-space QMC calculations?
13
votes
2answers
118 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
votes
1answer
36 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
35 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
28 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 ...
6
votes
0answers
24 views

For which materials is the Bethe lattice a good model to compute the density of states of the conduction band?

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....
14
votes
4answers
261 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 ...
5
votes
0answers
38 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. ...
10
votes
1answer
80 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 ...
17
votes
1answer
113 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
votes
2answers
494 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
votes
2answers
137 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 ...
5
votes
1answer
74 views

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.
12
votes
2answers
311 views

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-...
11
votes
1answer
62 views

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 ...
11
votes
2answers
136 views

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 ...
11
votes
1answer
87 views

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 ...
13
votes
2answers
209 views

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 ...
24
votes
2answers
2k views

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 ...
15
votes
1answer
68 views

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. ...
14
votes
1answer
56 views

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 ...
13
votes
0answers
97 views

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 ...
13
votes
1answer
120 views

How to make heterostructure/heterojunction structure?

How can I make a heterostructure or a heterojunction of ZnO/MgZnO for optimization with WIEN2k code?
12
votes
1answer
199 views

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 ...
11
votes
2answers
89 views

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 ...
16
votes
2answers
94 views

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 ...
14
votes
2answers
109 views

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 ...
14
votes
1answer
106 views

Can DFT be considered an ab initio method? [closed]

I have very little experience with DFT, but coming from more of a coupled-cluster background, where the improvements are "systematic", to me it seems that the choice of functional in DFT is somewhat ...
16
votes
1answer
76 views

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 ...
18
votes
2answers
103 views

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 ...
20
votes
3answers
135 views

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 ...
3
votes
0answers
50 views

In what kind of system, relativistic effect is non-negligible? [duplicate]

For electron with large kinetic energy, one needs to introduce Dirac equation for relativistic correction. In what type of systems these relativistic effects is non-negligible?
19
votes
3answers
167 views

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?
20
votes
3answers
177 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 ...
20
votes
1answer
100 views

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 ...
13
votes
1answer
89 views

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)?
24
votes
2answers
159 views

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 ...
20
votes
2answers
133 views

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^...
22
votes
2answers
128 views

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, ...