Questions tagged [density-functional-theory]

Density functional theory (DFT) is a quantum mechanical model used to estimate the electronic structure of molecules and condensed matter. In broad terms, DFT works by treating all the electrons in the system as a single electron density, and computing physical quantities of interest as functionals of that electron density. (from Physics.SE)

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Paper Data Replication

I read a paper recently - Here. I found the concept of Electride materials very interesting and wanted to mess around with them myself. I tried to replicate the partial electron density plots shown in ...
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Transition state and intermediate very close to each other

I've been studying a particular reaction with DFT, where a transition state and the following intermediate are very close to each other. The change in geometry is rather small and therefore the ...
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Why are correlation consistent basis sets used with DFT calculations?

Reading some papers, there is a bit of a curious observation that does not exactly make a lot of sense to me. In Quantum Chemistry, different methods exist to carry out geometry optimisation and ...
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Why does the local density approximation (LDA) overestimate atomization energy?

I have read numerous times that the local density approximation (LDA) overestimates atomization energy. For example, here is a quote from Dr. Burke's book: LDA typically overbinds molecules by ...
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d-orbital splittings in WS2 monolayer

The formerly degenerate $d$ orbitals of the tungsten atoms in the $\ce{WS2}$ monolayer are split into three groups: (1) $\mathrm{d}_{z^2}$, (2) $\mathrm{d}_{x^2-y^2}, \mathrm{d}_{xy}$ and (3) $\mathrm{...
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Coupling constant (Jab) - Why more unpaired electrons means a smaller coupling?

I hope this is not a "homework" question, but I'm having a bad time trying to figure this out. Available literature proposes 3 equations to calculate the coupling constant during a Broken-Symmetry ...
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Hybrid functional calculations using different approach

In hybrid functional such as B3LYP, PBE0, HSE etc, some part of HF exchange and/or correlation is added to some part of DFT X/C part in order to get better results. My question is if I am adding 1/4 ...
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Calculation correct binding energy for a system?

I am doing DFT calculations (VASP) to calculate correct binding energy for an amorphous silica surface and silver adatoms. From MD simulation, we found that a binding energy of 0.2 eV gives results ...
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How to run a B2PLYP-D3 calculation in Gaussian 09?

Can anyone help me to run a geometry optimization and frequency calculation using B2PLYP-D3 functional including the DFT-D3 dispersion correction? I went through Gaussian manual, however, it was not ...
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Optimization and DFT-D3 energy calculation in GamessFireFly version 8.1.1

My input was ...
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Density Functional Definition

Is it wrong to say that Density Functional means that Electron Density is a function of the orbitals (wave function) of all electrons in 3 dimensions, if so, why ?
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There are no wavefunctions in DFT

I have seen this phrase several times across DFT textbooks. However, I am not sure if it still holds. Was there a change or a theorem that proved it otherwise? Several programs display wavefunctions ...
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Estimating stability and mean life of anomalous tautomers

A pair of bases in the DNA, say, A-T, have a tautomerized form A*-T* (resulting from switching the sides of both protons along the hydrogen bridges). I have studied how, by means of DFT computations, ...
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DFT Code for Atoms : Sources

Some time ago I implemented the restricted and unrestricted Hartree-Fock methods. I had a lot of fun and I learned a lot. It goes without saying that Szabo and Ostlund's book "Modern Quantum Chemistry"...
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Warning during geometry optimization via Gaussian

I have some recurrent problem with my DFT calculations [functional: hseh1pbe; basis:6-31+g(d,p), object: porphyrin derivative]. During the MO setting I get: **** Warning!!: The largest alpha MO ...
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Ab initio effective potentials

I have been reading a journal article on ab-initio pseudo-potentials, and I need some help understanding it. The article is C. F. Melius and W. A. Goddard, III. Phys. Rev. A 1974, 10, 1528. A summary ...
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Where can I find a collection of density functional parameterizations?

I want to implement a solution to the electronic Schroedinger equation using DFT. I know there are many, many functionals to choose from but don't know where to start. I'd like to start with a couple ...
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Equivalent of Szabo and Ostlund book for DFT

Szabo and Ostlund book Modern quantum chemistry [1] is extremely useful to understand Hartree-Fock and post-Hartree-Fock methods. Not only it explains the theory behind such methods, but it is also ...
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Can PBE (and LDA) actually be a better choice sometimes?

Part of my work as an inorganic chemist is to investigate the magnetic coupling between metallic centers in coordination compounds. After some time, I've noticed that the classic PBE functional is the ...
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Better functionals to work with transition metals

My Masters in inorganic chemistry is focused in magnetic properties of transition metals; great part of the work is done with DFT methods using softwares like ORCA and NWChem, but since my University ...
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A thorough benchmark of DFT functionals without dispersion corrections

So, I'm looking for a benchmark of DFT functionals not including dispersion corrections. Something similar to Grimme's and coworkers GMTKN30 database, but for benchmark calculations done without ...
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Is There an Acceptable Potential Which Can Represent the Interaction between Finite-sized Ions?

The question is as mentioned in the title. Take for example the interaction between $\ce{Ar^+}$ and $\ce{Ar^+}$. In general, is there an acceptable potential which can represent the interaction ...
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Is density functional theory an ab initio method?

The following comment by Wildcat made me think about whether density functional theory (DFT) can be considered an ab initio method. @Martin-マーチン, this is sort of nitpicking, but DFT (where the last ...
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Electronic density distribution in hydrogen bond

I'm currently studying about the atomic configuration of electrostatic interactions. Concept is there that in case of interactions like in N-H...N-H (amides), the stability depends on the position of ...
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Difference between single point energy and dimerization energy

I am investigating potential energy surface characteristics of some electrostatic monomeric interactions e.g. $\ce{F-H}$...$\ce{F-H}$. I'm using DFT and SCS-MP2 to perform the necessary calculations ...
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Exchange-correlation hole

I did a google and chemistry.exchange search and found several technical definitions of the exchange correlation hole. The questions that I want to proposes are: What the exchange-correlation hole ...
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Most efficient level of theory for sulfur-containing proline analogues (one that will work)

I'm modelling a small set of proline analogues - extra functional groups, sulfur in the ring. Using Gaussian / DMACRYS. ...
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How to define custom force in quantum chemistry packages?

I don't know if this is really applicable but I want to add a custom force (say, $F(x,y,z)$) to some atoms in my geometry optimization. Is there any way to add such forces to the DFT or molecular ...
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DFT Functional Selection Criteria

I have a very very general question: In DFT functional selection , mostly people speak about the most recent ones. For example my professor always asks: " which DFT Functional did you select ? " ...
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Density Functional Theory with Generalized Gradient Approxmations (GGA) - What Happens if the Electron Density Shows a “Kink” at the Ion Position?

My question may be stupid, so please correct me if you find anything which is obviously erroneous. In the following I will place a question mark (?) besides points/steps I consider doubtful. My ...
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Signs of Exchange and Correlation Potentials

The exchange and correlation potentials refer to those defined in density functional theory. (See also http://en.wikipedia.org/wiki/Local-density_approximation) Define the exchange potential as $V_{x}...
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Which Basis Set is suitable For Mercury-complex in DFT calculations?

Which Basis Set is suitable For Mercury-complex in DFT calculations? Please provide the answers with any journal reference.
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Search materials by HOMO, LUMO and work function

I need to search organic semiconductors for organic photovoltaics (OPV) by their HOMO, LUMO, work function at 300K (as I understand, WF cannot be derived from HOMO and LUMO because semiconductor can ...
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DFT Calculations, Atomic Ionization Potentials — Which Exchange-Correlation Functional to Use, to Preserve Koopmans Theorem?

I have a program which can perform density-functional calculations for atoms, given a density functional. Of course the simplest form of exchange potential to use is one relevant for a uniform ...
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What do short-range and long-range corrections mean in DFT methods?

Currently I am looking for the most accurate calculation method for a simple non-conjugate molecule consist of C, N, O and H. Normally I would try each method for a similar and known molecule then ...
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How to simulate chemical reactions in GAMESS?

I am rather newb in GAMESS field but finally, learned to make input files for most molecular simulations and could even use TD-DFT for excited states (special thanks to Geoff Hutchison for his help). ...
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What is the difference between Dielectric and Capacitive Polarizable Continuum Model?

I have good background knowledge on Quantum Chemistry calculations but my knowledge on Solvation Models is not that amazing. Many times I read a paper that uses TD-DFT, they also assign some solvent ...
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Interpretation of TD-DFT results

For the first time I'm doing TD-DFT calculations (wB97XD functional) in Gaussian 09 for an open-shell system and the results look like the hell of a mess for me. The molecule is rather big, so I ...
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How do Quantum Software Packages Work?

If one wants to calculate a moderate size Alkane (with say 10-15 Carbons , assuming 100 electrons , with Restricted Hartree Fock based methods) we can simply say that electron-electron part will be $...
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Are there any full worked examples of DFT calculations?

I just started learning DFT and now I am totally confused. Assuming I want to use B3LYP: \begin{align} v_s\left(\textbf{r}\right) &= v_\text{ext}\left(\textbf{r}\right) + \int d^3r\frac{n\left( \...
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What's the difference between PBE and B3LYP methods?

I can't find an answer to that question. I was told that in B3LYP, more variables implemented in the method are empirical, but I can't find anywhere if it's true, and I'm sure it's not the only ...
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How to model iso-surface of molecular orbitals of singlet and triplet excited states

I've modelled the iso-surface of the highest occupied molecular orbital of a molecule with DFT in Gaussian.If I were to model the iso-surface of the molecular orbital of the singlet and triplet ...
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Defining and testing custom made DFT functionals?

What is a good and free software for this endeavor? Any recommended articles on the subject? I want to design dft functionals, trying out different parametrizations and optimizing mixing constants for ...
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DFT optimization of a molecule in gaussian and find electrophilic sides [closed]

I am not a pro, but I have some experience with gaussian. For example, I can optimize a structure, calculate the frequency and rotational energies. In the lab I made a nucleophilic substitution ...
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Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable method/...
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Why is Density Functional Theory notoriously bad at describing oxygen molecules?

I read in several papers that DFT is notoriously bad at describing free oxygen molecules but in none of them an explanation or reference concerning the problem has been provided. I guess this has ...
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Computing of strengthening of π-interaction

I need some practical advise. What would be the easiest approach to compute strengthening or weakening of π-interaction in a bond with multipole-bond character. I'm not really fond of going through ...
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How should I go about picking a functional for DFT calculations?

I've been looking to use time-dependent density functional theory, but reading the literature I keep getting overwhelmed by how many different functionals there are. How should I go about selecting ...
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Predict XPS Spectrum of Organic Monolayers on a Semiconductor

X-ray photoelectron spectroscopy (XPS) is a particularly useful technique for examining the surfaces of all sorts of materials. Organic monolayers are particularly difficult to characterize completely ...
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Striking examples where Kohn-Sham orbitals clearly have no physical meaning

In Density Functional Theory courses, one is often reminded that Kohn-Sham orbitals are often said to bear no any physical meaning. They only represent a noninteracting reference system which has the ...

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