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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Gaussian16 Raman calculation from IR checkpoint file?

I already did an IR frequency calculation for my molecule. Is there any possibility to just run a Raman frequency calculation with the chk file from my IR calculation? - or have I to do the ...
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Charge and multiplicity in Gaussian16 calculations

I like to perform a calculation with pyridine and connected to the nitrogen to a gold atom. Now I think about the charge and multiplicity. Can anyone tell me a paper or book to read about how to ...
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Simulation of Pyridin attached to gold atom

I would like to simulate to get the influence of a gold atom on the oscillation modes of pyridine. I have already carried out simulations in which there is a coordinative bond between nitrogen and ...
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Best way of studying protonation in non-polar solutions with ~100ppm of water present using computational methods?

I am currently looking at the mechanism of the formation of storage deposits in jet fuel. Interestingly, the concentration of acids in the fuel correlates strongly with the total insolubles formed ...
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Ab initio molecular properties which can be experimentally measured and don't require derivatives/gradients

I'm attempting to teach myself HF and DFT by implementing various algorithms, but I've run into a snag: many molecular properties which are experimentally measurable appear to require taking gradients,...
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Chemical accuracy and room temperature

Chemical accuracy is $\pu{2E-2 eV}$ but room temperature $\pu{20 ^\circ C}$ is $\pu{2.5E-2 eV}$, so why is it not necessary to take into account thermal effects in DFT? I understood (maybe wrongly) ...
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'Ab initio' couplings for DNA used in charge transport

I came across a publication by Senthilkumar et al. [1] in order to compute charge transfer through the DNA. Table 3, for instance, gives the coupling between bases along the leading (or retarded) ...
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GGA functionals requiring second derivatives?

In "Lecture Notes in Quantum Chemistry II" from the European Summer School in Quantum Chemistry, the authors note that when discussing the LYP functional and other GGA functionals, that ...
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Quantum calculation of free energy change in neat conditions

I am slightly baffled by a seemingly simple situation: I want to calculate the free energy of association between a molecule $\ce{A}$ and the solvent $\ce{B}$ using quantum methods (e.g. DFT). From ...
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Transition State search

I've been trying to find a transition state for the reaction of Pd + F2 with no luck. Has anyone ever tried a similar reaction, have they managed to get the TS? The reaction proceeds from the ...
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Why does DFT-D finds different optimized geometries for the same structure when using different input geometry files?

When I change c lattice parameter and optimize the structure with DFT-D, every time I get a significantly different geometry with different energy? Why is this happening with DFT-D?
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What are the rules for constructing Kohn-Sham orbitals?

I just recently began to study quantum chemistry and need some clarification for the construction of Kohn-Sham orbitals. Consider a system of several atoms. Let there be $N$ electrons in this system. ...
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High-temperature DFT

Why is it so difficult to perform DFT calculations that consider temperature? I have seen that time-dependent DFT is needed to model systems at high temperature. Why is this the case? What about ...
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Does the amount of solvent interaction energy depend on the absolute gas phase energy?

I've been performing Gaussian 16 DFT optimization and single-point energy calculations on different conformers of a rather large organic molecule. My first series of calculations was without solvent ...
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Laplacian of the Hartree Fock second-order reduced density matrix

I am attempting to replicate and understand the Colle-Salvetti method for approximating the electron correlation energy.[1] I have successfully replicated the method, but there is one part of the ...
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I'd like to model some compounds with DFTB, but some elements don't have parameter files in the official site. Is there a workaround?

I was reading a bit about this technique, Density Functional based Tight binding (DFTB). It's claimed it can provide a speed improvement of several fold when compared to plain DFT, still giving ...
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Would there be need for periodic DFT if we are able to get all the forcefields of all the elements in the periodic table in ReaxFF?

Since ReaxFF combines the advantages of DFT and Classical MD, would there be any need for periodic DFT calculations if we can have all the forcefields of all the elements of all the possible systems?
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Is there any software that can do geometry optimization using machine learning?

DFT is a computational tool that is used in optimizing and calculating the electronic structure properties of molecules. Are there any machine learning codes that can do something similar in a ...
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Trouble understanding equation from density functional theory

In the review by Oliviera et. al., I do not understand how the authors get equation 14: \begin{equation} E[\rho]=\sum_i^Mn_i\langle\Psi_i|-\frac{1}{2}\nabla^2+v_{ext}(\vec{r})+\frac{1}{2}\int\frac{\...
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What are the cheapest basis sets able to model intermolecular dipole interactions inside a metal complex and give good relative energies, with DFT?

As a example, If I have a square planar complex of a cation with both a weakly polar ligand (X) and strongly polar ones, like ammonia and water I expect a bit of stabilization due to formation of a ...
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Generate Surface with CubeFile from Gaussian in VMD or other free programm

I asked a question before, about how to save a mapped surface from GaussView. I don't get an answer, so I get much deeper in my internet research about it again. Now I want to try to create a mapped ...
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Is this approximate equivalence table between Pople's basis sets and Jensen's DFT attuned polarization consistent basis sets (pcseg-n) correct?

I have some calculations results I runned previously using Pople's basis sets, mostly 6-311+G(d), under Gaussian09. These days I read some texts on Frank Jensen's family of polarization consistent, ...
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How to extract a image (vector graphic) from a surface EPS plot with GaussView?

I am quiet new to this field of chemistry. I work with GaussView and I created a surface plot for my molecule with the cube and surface generator. This works very well. Now I like to save and copy ...
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Is Tkatchenko's MBD-NL method self-consistent?

I have a question regarding Tkatchenko's [1] new nonlocal many-body dispersion method (MBD-NL). Does anyone know if it's a self-consistent method? I read this paper many times but I'm still not sure. ...
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Can density functional approximations including dispersion correction perform worse than without it?

I am trying correlate some experimental properties of a molecule to its calculated equilibrium geometry. To do so, I calculated the geometry and energy of some conformers. Now, I obtain mixed results ...
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Can you explain DFT and TDDFT functioning (math aside)? [closed]

I have been recently reading a lot on the quantum mechanical theory regarding Density Functional Theory, DFT, and Time Dependent Density Functional Theory, TDDFT (Oscillatory and Rotatory Strengths in ...
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Question about the setting of DFT (Density Function Theory)-NEB (Nudged Elastic Band) calculation

I'm attempting to calculate Mg ion vacancy migration inside Pyrope unit cell. System has total 159 atoms, beginning and end geometry is optimized. For intermediate image, I'm using one coordinate that ...
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High errors in frontier orbital energy calculation using DFT

In a recent paper by Faber et . al., Mean Absolute Error and DFT (B3LYP) error (relative to the experiments) for 9 properties of QM9 dataset molecules has been reported. \begin{equation} \begin{array}...
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How to do RPA (Random Phase Approximation) in VASP?

I'm new to VASP and as such don't know much of its intricacies yet. I want to find out the interlayer binding energy of a given molecule and to do that I already opted for the use of different ...
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On mathematics behind molecular orbital energies

When explaining the mathematics behind calculating molecular orbital energy , namely HOMO and LUMO energies, using quantum chemistry, Chainer Chemistry documentation states that From mathematical ...
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How to find a full electron basis set that approximate a given ECP basis set?

In computational chemistry of transition metals, there are many popular basis sets, from pople+LANL2DZ mixed basis sets, to Ahlrich and Karlsruhe basis sets like def-SVPD, def2-TZVPPD. Often the ECP ...
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Global reactivity parameters from open shell DFT calculations using Koopman's theorem

Koopmans' theorem is a useful approach to calculate the global reactivity parameters from the HOMO-LUMO energies. My question is, does it apply to the open-shell systems where we get two sets of ...
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Which DFT functional is best for predicting macroscopic properties of molecular liquids?

Which DFT functional (KS-DFT, to be more specific) performs best at predicting macroscopic properties (density, surface tension, boiling point, relative permittivity etc.) of molecular liquids (...
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Finding mathematically the ground state density in DFT

To find the ground state density in DFT, you set the following Lagrangian: $$L = E[\rho(\vec r)] - \mu\left(\int \rho(\vec r) \mathrm{d}\vec r - N\right)$$ While minimising with respect to the ...
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DFT vs. MP2 for stacked dimer

Recently, I looked at these two papers analyzing the excited-state properties of modified DNA bases (2-aminopurine and 8-vinyl-A) and how they are influenced by stacking with natural nucleobases: ...
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How can I obtain the wave function of the dihydrogen system, by hand using Self Consistent Field DFT calculations? [duplicate]

After doing some energy calculations for the $\ce{H2}$ system in Gaussian, using ωB97X-D/STO-3G level of theory, and generating a .wfn file, I wanted to understand better how the computer does ...
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How to account for solvation of a molecule explicitly in quantum calculation?

I'm looking for a way to account for hydrogen bonds formed with my molecule in aqueous solution explicitly in DFT calculation. I'll do it in order to compare stability of two structures in water. As ...
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How to calculate the amount charge transfer from a natural population analysis?

I am trying to reproduce the quantity referred to as the degree of charge transfer reported in this publication by Zhu et al. [Ref. 1] for the F4-TCNQ molecule. I am interested in section 3.2 in the ...
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How can I find the smaller symmetric structure from big crystal unit cell?

I have Pyrope (Mg3Al2(SiO4)3) crystal structure, downloaded from materialsproject: https://materialsproject.org/materials/mp-6073/# It appeared as triclinic cell, but if you download CIF file and ...
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What is meaning of LAV2P basis set?

I am working on energy optimization of molecular structure using DFT with Schrödinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set ...
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Can I compare DFT calculations with different grids?

When doing DFT calculations, some integrations are commonly done numerically on grids. [In fact, more than a single grid may be used at the same time for different integrals, e.g. approximations such ...
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How one can calculate Si-O-Ca/Mg valence angle energy?

I want to perform the relaxed scan (or relaxed surface scan) for the valence angle energy of Si–O–Ca, Si–O–Mg, Al–O–Ca, and Al–O–Mg. I will use DFT (ORCA), probably B3LYP and triple zeta basis set (...
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Guide to DFT functionals [duplicate]

Having recently begun studying Quantum and computational chemistry in depth... I am looking for a manual, text, or guide of any form that could explain the basic formulations and potential of the ...
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Limitations of extremes for the exchange-correlation functional - DFT

In DFT the exchange-correlation function is critical for the correct description of the system. I have a question about the applications and shortcoming of some functionals. LDA delocalizes electrons ...
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Getting radial Kohn-Sham orbital from the output of an electronic structure code using gaussian basis sets

As we know that in solving the Schrodinger equation (Kohn-Sham equation), we expand the wavefunction in terms of some basis sets and them optimize the energy (the expectation value of Hamiltonian) by ...
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Is there an easy explanation of MP2 calculation [closed]

for my master thesis I calculated some ring strains with MP2 calculation. It was not hard to calculate these things but I'm struggling to understand what the theory is about. Now I'm defending my work ...
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DFT Exchange-Correlation Two Electron Integrals

Are there any electronic structure programs that print the exchange-correlation (XC) integrals for a given DFT functional? These integrals are of the form $$\langle pq|w|rs\rangle$$ where $w$ is an XC ...
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What's the most complete basis set for calculating chemical shifts with DFT?

I'm trying to benchmark some NMR chemical shifts. The literature suggests that the pcS-4 basis set will be the most accurate. I was wondering if there were any basis sets that are more complete than ...
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Reference states for molecular orbital energies in DFT calculations

When doing a population analysis using density functional theory (specifically as implemented in Gaussian), what are the orbital energies (i.e. alpha and beta eigenvalues) with respect to? If I have ...
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Why can we know a materials properties by knowing its ground state at 0K - DFT

I have had this doubt ever since I was introduced to DFT. For what I gathered whatever results you obtained with DFT (by using VASP, quantum expresso or any other software) you can say those ...