24 votes

What are the types of charge analysis?

Bader charge analysis In Bader's theory of Atoms in Molecules, we partition a molecule into "atoms" which are separated from each other by surfaces of minimum charge density:                 ...
I have no free time anymore's user avatar
23 votes

What are the types of charge analysis?

Just to add to the discussion: Mulliken charges are flawed in many aspects, but we know how and why, and therefore we accept its use, since it is simple and easily computed. But very dependent on the ...
MSwart's user avatar
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20 votes

What are the types of charge analysis?

Hirshfeld / CM5 (Charge Model 5) My main interest is in explaining CM5 charges, but to do that it's necessary to briefly explain what Hirshfeld charges are. Hirshfeld charges are obtained as: $$q_X=...
Tyberius's user avatar
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20 votes

What are the types of charge analysis?

Electrostatic potential (ESP) derived charges Note that ESP1 derived charges include ChelpG (CHarges from ELectrostatic Potentials using a Grid-based method), the Merz–Kollman (MK) 2, and the RESP (...
Cody Aldaz's user avatar
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18 votes

What are the types of charge analysis?

Mulliken population analysis The Mulliken charge scheme is based on the Linear Combination of Atomic Orbitals (LCAO), so, it is based on the system wave function and was described in a series of ...
Camps's user avatar
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18 votes

What are the types of charge analysis?

To give a example of the "random number generator" behavior of Mulliken charge analysis pointed by @SusiLehtola, below I'm showing the results of some test runs I did before on the CO2 ...
ksousa's user avatar
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18 votes

What are the types of charge analysis?

Mulliken and Löwdin population analysis In the atomic orbital basis set (enumerated in Greek indices), one finds that the number of electrons $N$ is equal to the trace of the product $\mathbf{PS}$ $$ ...
TAR86's user avatar
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14 votes

What are the types of charge analysis?

Voronoi charges Voronoi charges (here called VC) are based on the partition of the real space in a system into Voronoi polyhedra.$^1$ A given point in space belongs to the polyhedron of some atom if ...
TAR86's user avatar
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12 votes
Accepted

Bond Order: When and how is it used today?

Why Bond Order? Bond order isn't terribly useful to a computationalist directly; however, it can be invaluable for translating Quantum Mechanical results into a framework thats readily understood by ...
Tyberius's user avatar
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12 votes

What are the types of charge analysis?

Don't use Mulliken for charge analysis. It is basically a random number generator, since it lacks a basis set limit. By choosing a different basis set representation, you can basically freely move the ...
Susi Lehtola's user avatar
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11 votes

What are the types of bond orders?

Wiberg (1968) Let's start with the "classic" bond order paper by Ken Wiberg (born in 1927 and still alive!). The Wiberg Bond Index (WBI) between fragments A and B of AB is calculated as ...
I have no free time anymore's user avatar
11 votes
Accepted

How can reactivity indices be calculated in a time-dependent scheme?

Time-evolution of conceptual DFT quantities has been considered starting, I think, with Chattaraj ~2000. (I imagine there is some earlier work by Ghosh and/or Harbola, but I do not know a reference.) ...
Paul Ayers's user avatar
10 votes

What are the types of charge analysis?

Density-Derived Electrostatic and Chemical approaches Net atomic charges have two primary applications (dual use): to quantify charge transfer between atoms in materials; this identifies cations and ...
Thomas Manz's user avatar
9 votes
Accepted

How to take periodic snapshots while running a simulation in VASP?

There is no way to do this directly in VASP, but you can achieve this goal using the Atomic Simulation Environment (ASE). With your OUTCAR available, do the ...
Andrew Rosen's user avatar
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8 votes

What are the types of bond orders?

How to test bond order methods for chemical consistency Some of the bond order methods that claim to work do not give consistent results across different SZ values of a spin multiplet or different ...
Thomas Manz's user avatar
8 votes

What are the types of bond orders?

Laplacian Bond Order This method is an extension of the QTAIM (Quantum Theory of Atoms In Molecules) concept of using the Laplacian of the electron density $\nabla^2\rho$ to characterize bonding. ...
Tyberius's user avatar
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8 votes

What are the types of bond orders?

It depends on what you want from it. If you're an organic chemist, you'd be mostly interested in the type of bond (single, double, triple, aromatic), and for that the bond order is most relevant (but ...
MSwart's user avatar
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8 votes

Are there properties that can only be calculated with a given set-up?

Only a partial answer: some setups are surely better suited than others for a given property. Some developers recognize this and thus do not bother implementing properties for which their setup will ...
TAR86's user avatar
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7 votes

How to take periodic snapshots while running a simulation in VASP?

In can be done easily using python or bash script. You have to keep looking for changes in OSZICAR. Whenever OSZICAR prints 'F' i.e. end of electronic self ...
Pranav kumar's user avatar
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7 votes

Does integrating PDOS give total charge of a system?

You shouldn't integrate to the Fermi energy, unless you want the T = 0 K result and that was what you computed with your DFT program (which is actually quite difficult to get). The correct expression ...
Phil Hasnip's user avatar
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7 votes

Bond Order: When and how is it used today?

I disagree with the statement by Tyberius that: "Bond order isn't terribly useful to a computationalist directly; however, it can be invaluable for translating Quantum Mechanical results into a ...
Thomas Manz's user avatar
6 votes

Bond Order: When and how is it used today?

An interesting application of bond orders in reactive molecular dynamics simulations is the ReaxFF force field, where the MD force field parameters are optimized by ab initio simulations. To quote one ...
Arc's user avatar
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6 votes

Total number of electrons from DOS and PDOS - what's the theory behind it?

If you integrate the DOS, $g(E)$, up to the Fermi-level, $E_F$, the area should be very close to the number of electrons, $N$; i.e. $$ N \approx \int_{-\infty}^{E_f} g(E) dE \tag{1}. $$ You'll have to ...
Phil Hasnip's user avatar
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5 votes

Can the Electron Charge Density (ECD) have negative values and why?

Yes, it is possible to get regions of negative electronic charge density when using PAW or USP pseudopotentials. The reason is that these pseudopotentials take the "soft" charge density (the ...
Phil Hasnip's user avatar
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4 votes
Accepted

Elastic Calculation and dipole tensor calculation using VASP

We already have lot of discussion on calculations of elastic constants using stress-strain relationship or energy-strain relationship Problem related to the calculation of elastic constant with VASP5....
Pranav kumar's user avatar
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4 votes

Is there any free software that helps to know specific charge densities or ELFs at any position of the material?

Yes, for example the Python package chemtools gives several examples of calculating the ELF from a Gaussian cube or similar wavefunction file. At the moment, it will generate a Gaussian-compatible ...
Geoff Hutchison's user avatar
3 votes

How to calculate the individual atomic charge from a cube file of charge density?

I do not have a python code for you. But I could direct 2 post-processing open software you could use to calculate individual charge of your atoms. (1) MultiWfn (http://sobereva.com/multiwfn/) (2) ...
danjodc's user avatar
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3 votes

What is the basic equation for total charge calculation from a 3D cube file of charge density file?

The cube file contains the density for each grid point. The general formula for calculating the total number of electrons for that unit-cell would be: $$ n = \iiint \rho(x,y,z)dxdydz $$ Each grid ...
nickpapior's user avatar
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2 votes

What does the "atomic pseudo charge-density" in the POTCAR file stand for?

I'm not a VASP user, so I don't know for certain, but I expect that it contains the atomic pseudo-charge density on a radial grid, using logarithmic coordinates. This is the usual way to express the ...
Phil Hasnip's user avatar
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