15 votes
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What does machine learning learn about DFT?

Total energies and HOMO-LUMO gaps are very different quantities, and naturally necessitate very different neural network designs (including the choice of descriptors and architectures) in order to ...
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  • 7,233
15 votes
Accepted

Artificial intelligence is a hot topic, but should I pursue it if I'm interested in Matter Modeling?

"I am a student now and should decide my major to research soon. AI/ML is a very hot research field and I am very interested in it, but I have some doubts before I study AI/ML." AI is ...
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  • 28.8k
9 votes
Accepted

Is it possible to calculate the pka value of different H atoms on one molecule?

Yes. Simply calculate the pKa from the definition: $$ \rm{pK_a} = \lg \frac{[AH]}{[A^-][H^+]} \tag{1} $$ The equilibrium constant in the logarithm is computed from the Gibbs free energy of the ...
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  • 7,233
8 votes

What does machine learning learn about DFT?

It could just be that the features you are using are well suited for describing total energies in these sorts of systems, but not in describing the differences of eigenvalues. When people do ML to try ...
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  • 506
8 votes

Artificial intelligence is a hot topic, but should I pursue it if I'm interested in Matter Modeling?

I did my master's research project in predicting absorption spectra using machine learning (with fingerprints). So, my research is somewhat in the field of material modelling you can say. I want to ...
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  • 5,754
7 votes
Accepted

SOC calculations in VASP

Sometimes the forces will be similar with and without SOC, so you can relax without SOC, and then do a single point calculation on the relaxed structure with SOC. When you do that calculation, you ...
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  • 506
6 votes

What is the physical meaning of the term "non-local interaction"?

The non-local operator in Hartree Fock is the Exchange operator. Locality is a mathematical property. Look at the Coulomb operator first which acts like this: $$ \hat v_H\;\varphi_s(r) = \sum_i^{N_\...
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6 votes
Accepted

How to find which atoms/bonds contribute to the particular section of band structure?

You can calculate an orbital projected density of states and band structure to see what atomic states correspond to features in the DOS and band structure. That’s one of the things that they plot in ...
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  • 506
5 votes

Which functionals should I include for a simple hydrogen atom system?

As far as I know, the issue of the kinetic energy functional is how people first came to use orbital based functionals in any capacity. Meaning the von Weizsäcker functional, albeit the best orbital ...
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4 votes

Artificial intelligence is a hot topic, but should I pursue it if I'm interested in Matter Modeling?

While machine learning is becoming very important, I think physics-based models continue to be necessary in matter modeling. ML models are good for systems where there is a lot of data available. On ...
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3 votes

TBT Transiesta Calculation error

I will quote the manual. :) It is extremely important that the electrodes only interact with one neighboring supercell due to the self-energy calculation[1]((http://iopscience.iop.org/0305-4608/15/4/...
3 votes

What happens to the position coordinates of the nearest neighbors in supercell studies?

DFT calculations based on a supercell method utilize the periodicity of a perfect, infinite lattice by imposing periodic boundary conditions onto the wavefunction of the system (Bloch's theorem). In ...
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  • 310
3 votes

Is there an example in which TD-DFT was successful in describing photophysical or photochemical processes?

A recent non-obvious one has been the use of TD-DFT to look at vibrational couplings in singlet fission in pentacene. The sequence of electronic transitions works like this: Optical absorption ...
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3 votes

What is the physical meaning of the term "non-local interaction"?

It's all hollow words if no proper definition is given. The definition I know is the following: For a one-body operator $A$, define $$A(x,x^\prime):=\langle x|A|x^\prime\rangle \tag{1} \quad . $$ We ...
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  • 453
2 votes

3D band structure plot

Usually people just do it by picking a path through the Brillouin zone and then plotting it in one dimension. You can use the seekpath or pymatgen (I think pymatgen has this) tools to generate paths ...
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  • 506
2 votes

Create doped structures to POSCAR files for vasp

Cluster Expansion Codes Several codes can help with fitting a cluster expansion (CE) to this problem. A cluster expansion uses (small-cell) computed DFT energies and maps them to short-range multi-...
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2 votes

Issues converging with DFT+U and magnetism in Quantum ESPRESSO

As a solution, you should check if convergence is difficult due to the magnitude of your Ru U correction. Try smaller corrections and see if that helps. You can also try applying a correction to the ...
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1 vote

Why Kohn-Sham equations are regarded as single-particle equations?

I would argue that because the exact potential, like the ground state density, is a property of the system. The Hohenberg-Kohn theorems show that there is a scalar single-particle potential $v({\bf r})...
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  • 14.7k
1 vote

What happens to the position coordinates of the nearest neighbors in supercell studies?

In solid-state calculations, DFT code does not know whether you give it a crystalline unit cell or a supercell. Instead, it treats every input structure as a "unit cell". So my answer is &...
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  • 139

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