Density functional theory Puns

DOI: https://doi.org/10.1021/acs.jctc.5b01082

URL: https://pubs.acs.org/doi/abs/10.1021/acs.jctc.5b01082#

I want to run simulations using DFT. But as of now I only have a basic understanding of quantum mechanics ( upto two particle systems, 5th chapter from griffiths ) ane a basic understanding of hartree cock approximations do I need anything else or should I study something first before diving deep

I'm a first year PhD student in inorganic synthesis but I've recently been trying to add some computational skills to my repertoire. I have had no prior computational experience, and so a lot of the things I'm trying to learn are going over my head.

Right now, I'm a bit confused about how one goes about determining which functionals and basis sets are appropriate for their calculations. Is there a cheat-sheet/table/review paper out there that outlines the situations in which you would choose specific functionals & basis sets (e.g. "You should use B3LYP if A/B/C, M06 if D/E/F)?

Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c09041

Thijs Stuyver and Sason Shaik

https://ift.tt/2IvAgfg

I am interested in materials from first principles. I learnt density functional theory (Quantum ESPRESSO) for materials modelling. I don't understand the difference between quantum many-body theory and density functional theory. In DFT, we use Kohn-Sham equations to show that the potential experienced by electrons in a crystal structure is a functional of their electron density. The exchange-correlation potential between electrons is unknown (we try to guess it).

I am a mechanical engineer and learnt DFT from YouTube and a short internship with a small research group. I will be very grateful to someone who can explain to me difference between quantum many-body theory and density functional theory. I feel like I am missing something but don't know exactly what.

I know what is DFT, but how exactly would I use it? What kind of problems I should/could look and think "hey, I could do DFT calculations on this" and how exactly would I proceed? If someone could link me to a real example of DFT being used to solve some chemical problem, I'd be eternally thankful.

What is the difference between time-dependent density functional theory (TDDFT) and molecular dynamics (MD)? What are some limitations of each? I know that TDDFT can be used to calculate excitation energies. I have heard that MD can be used to see how the atoms in a molecule move. I guess I'm just confused on the word "time" since MD depends on time as well but maybe in a different sense?

Or how do we experimentally measure the values that density functional theory produces? I’m not really sure what these values are besides that they are certain kinds of energies, I think. I guess band gap would be one example of a value DFT can predict.

Density functional theory (DFT) gained popularity in the 1970’s as an approximate but faster way to model molecules and their properties and still remains an industry standard.

It’s in contrast to using excact, but much slower (up to years waiting for computers) methods of modeling.

But now that the quantum computing age is upon us, will we go to the exact way of modeling these molecules?

I ask this out of self-interest, as I am choosing my graduate studies path and was leaning toward DFT but don’t want to spend time learning a potentially obsolete skill.

I would need to Supporting Information of this article:

On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization

T. L. Jacobsen, M. S. Jørgensen, and B. Hammer

Phys. Rev. Lett. 120, 026102 – Published 12 January 2018

DOI: 10.1103/PhysRevLett.120.026102

https://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.120.026102

I'm a 3rd year in Aerospace but looking into materials research in aerospace applications. My professor wants me to look into DFT and the vasp program but the manuals are very dense and difficult to absorb.

My current understanding is that you input atomic/electronic positions of a unit cell, tell the program how you want to deform it, then the program applies a periodic condition and outputs a result that you asked for, is this correct? Thanks in advance.

Hello! I am trying to replace a DFT funcional with a neural network. I've been doing it with a smaller data set and I worked so far. My new problem involves a input data of 3 x 1016222 and an output of 1 x 1016222. The three parameters of the input are U (from 0 to 20), n (from 0 to 1 for each U value) and m (from 0 to n, for each U value). I guess it's a kind of function aproximation problem, once what I want is to reproduce data within the input range.

I've been using Trainlm with NNTool, but I heard that Levenberg-Marquart isn't that good with large-sized networks and traingd/gdm it doesn't handle my data well.

So how I optmize computational and time cost with a very large matrix like these? I've been using a architeture with two hidden layers with 10 and 5 neurons, but I am unsure about these numbers.

U	    n	       m	    Total Energy
0,2	    0	       0	            0
0,2	    0	       1,53E-13	   -1,1037E-06
0,2	    0	       1,44E-13	   -1,1037E-06
0,2	    0	       1,42E-13	   -1,1037E-06
0,2	    0	       1,40E-13	   -1,1037E-06
...
0,2	    0,56413	   0,2438	    0,927427491
0,2	    0,56413	   0,2495	    0,923968253

U,n,m are the input parameters and E is the output. It goes something like this from U to 0 to 20, n goes from 0 to 1 for each set of U, and m goes to 0 until equals n (equals 1).

So I can follow the Hohenberg Kohn Theorems

E = E[n(r)] and E0[n(r)] = min <H> over n(r)

In a lot of derivations of the Kohn Sham equations, I see some steps involving the Lagrange multiplier method, but since we do not know how to write <T> explicitly as a functional of the density, it doesnt work out. This is done for both an electron non-interacting and interacting systems to show that they have the same form. The related SE equations are the KS equations.

1. What is the purpose of the Lagrange multiplier portion of the derivation?

2. Is the KS formulation just an perturbation-esque expansion with the non-interacting system as the starting point?

3. Is whole exchange correlation functional just a consequence of sweeping everything we dont understand into one pile (the portion of the Kinetic energy missed by the non-interacting system, the election-electron self-interacting portion, the quantum election-electron interacting bits (having to do with electron being a fermion), etc)?

4. How does the KS equations guaranteed an energy minimized electron density? (I think this is probably somewhat off topic, because this is probably related to variation calculus)

Hey r/physics!

I am a fourth year physics grad student focusing on computational condensed matter physics. I have used density functional theory to model solar cell and battery materials. Now that I am a good ways along my PhD I am fairly sure that I do not want to pursue an academic research position.

My interests in the last year have switched to machine learning and data science. I have taken some classes and plan on putting together some projects while finishing up my thesis to help with job prospects.

I was fairly fortunate to get some early publications in my research work and I am on my last project now. I mostly stuck it out because I got a good head start in the field and felt like it would be foolish to leave.

Was this a mistake? From my initial search job prospects in DFT outside academia are not very common and it seems like people expect a lot of background work when switching fields. Has anyone had any experience with this?

The reason I'm asking is that I have an opportunity to help him out as a first year Physics student. I know nothing about quantum mechanics(or any remotely advanced physics), and he said that if I wanted we could start gradually. He would answer my questions and guide me through the work.

Basically, it would be amazing to work with him, but I don't know how much I'd actually be able to help. It's theoretical physics and involves a lot of programming, of which I know nothing. Therefor, it might be months and months before I actually can start legitimately doing anything. Conversely, I could work other professors, that don't have as impressive as a resume(but are still all probably brilliant). I think their work would be much easier to start helping with.

Do you think it would be worth it to go for broke with Dr. Perdew? Keep in mind I don't even know if I'm smart enough to handle advanced quantum physics.

EDIT Forgot to mention, I already got another degree, and am going back for Physics. So I'll only be in undergrad for 2-3 years.

Thank you.