Linked Questions
27 questions linked to/from DFT Functional Selection Criteria
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Which MO approximation best fits with lab results and observation? [duplicate]
I understand that there are many different methods that can be used to approximate the set of MOs for an arbitrary molecule, as the actual quantum mechanical description is taxing to calculate. I just ...
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36
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3
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14k
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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 ...
- 44.4k
26
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5
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35k
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Comparing the stabilities of allylic, benzylic, and tertiary radicals
Which is the most stable free radical among the given species?
(1) $\ce{CH2=CH-CH2^.}$ (allyl radical)
(2) $\ce{C6H5-CH2^.}$ (benzyl radical)
(3) $\ce{(H3C)3C^.}$ (t-butyl radical)
(4) $\ce{...
- 2,063
28
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60k
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Rationalising the order of reactivity of carbonyl compounds towards nucleophiles
This is immediately following ron's answer from Why is a ketone more nucleophilic than an ester?
One of the most simplest questions you can ask, how can you rationalise the order of reactivity ...
- 44.4k
18
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2
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7k
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Dipole moment of cis-2-butene
I need someone to back me up on this before I go confront my teacher:
I was doing some analysis of the dipole moment of cis-2-butene.
Let's say that the alkyl groups are both on top.
Would the dipole ...
- 1,845
17
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2
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2k
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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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26
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2
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2k
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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 ...
- 1,552
19
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3
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750
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Do modern dispersion-corrected DFT methods give more accurate molecular geometries?
I was discussing with a colleague the use of modern dispersion-corrected density functionals. I take it almost as a given that the methods generally produce "better" (for some definition) geometries, ...
- 28k
13
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1
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10k
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Rationalizing the Planarity of Formamide
In formamide, the nitrogens appear to be $\ce{sp^3}$ hybridized, implying tetrahedral geometry. However, analysis shows that the molecule is actually very nearly planar with bond angles close to 120 ...
- 19.2k
12
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1
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How to choose the best method and basis set for a calculation in computational chemistry?
In Quantum chemical calculations, it is not always the case that the more complex (correlated) the method or the basis set the more accurate the results.
For example, it's sometimes found that MP2 ...
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12
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1
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1k
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"NBO diagrams" versus MO diagrams
Molecular orbital diagrams are well known by chemists.
According to Wikipedia (emphasis mine),
A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical ...
- 2,883
12
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2
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757
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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 ...
- 505
7
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1
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4k
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Calculating singlet-triplet gap and open-shell singlet character
I am trying to calculate the singlet-triplet energy gap ($S_0-T_1$) of a conjugated system (18 atoms). For the singlet $S_0$ state, assumed to be closed shell, the Gaussian options were
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- 314
8
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1
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1k
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How to obtain curve energy and non-bonded interaction parameters (e.g. Lennard Jones parameters) with Gaussian?
I am parameterizing a force field and would need to obtain non-bonded interaction parameters of atoms (e.g., Lennard-Jones parameters).
My primary idea is to obtain a potential energy curve using the ...
- 321
4
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1
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1k
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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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8
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1
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2k
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How to interpret the relation between CO stretch frequencies and backbonding strength for polycarbonyl compounds?
I am working on a series of octahedral complexes of the type $\ce{[M(CO)2(CH3)X3]-}$ where $\ce{M} = \ce{Co}, \ce{Rh}, \ce{Ir},$ and $\ce{X}$ is a range of ligands (halide, cyanide, nitrosyl, etc.). ...
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3
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1
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2k
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Periodic boundary conditions in DFT for cylindrical system
As I understand it, a DFT calculation uses periodic boundary conditions, whenever you want to simulate a bulk material. This is convenient because all information can then be extracted from the ...
- 151
3
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1
answer
536
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Is it rigorous enough to change a DFT functional after geometry optimization to calculate excited state properties?
I have done the geometry optimization with the B3LYP functional, however, there is a need to calculate the excited state energy, so the CAM-B3LYP functional should be better suited for that. Do I need ...
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8
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1
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482
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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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5
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1
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Gaussian parameters for IP and EA calculation
I have already calculated ionization potentials (IP) and electron affinities (EA) for a whole bunch of organic molecules (from around 20 to 25 heavy atoms, mostly carbon atoms, just a few oxygen or ...
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0
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1
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301
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Apparent inversion of oxidation state of sulfate ion using minimal basis set
It is well known that the sulfate ion has essentially no 3d-2p bonding; hence I used the minimal basis set(STO-3G) for the NBO calculation I did via Gaussian, just to check it.
However, I got a ...
- 725
5
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1
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158
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Which quantum chemistry approximation to use?
I'm just getting started with quantum chemistry using some simple test problems. I have a few of the software packages installed (ASE, Psi4, GPAW etc) and everything is working - no issues with the ...
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4
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1
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86
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How do I find the geometry of a tetramer assembly?
What's the best way of finding optimal geometry and minimal energy for tetramer with H-bonds? I know where H-bonds should be, but do not know their length.
Should I just draw randomly 4 molecules, ...
- 151
6
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1
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140
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Should I include solvation in quantum chemical calculations of a simplified protein-ligand interactions?
I am running a B3LYP-D3/6-31+G geometry optimization of a protein-ligand interaction. Well, not quite, I have simplified the protein to four amino acids surrounding the active site, but I keep the ...
- 4,773
0
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1
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72
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Which of the free access molecular modelling program apply the B3LYP/G-31G(d,p) level of theory?
Please, let me know which an open free molecular modelling program will apply
the B3LYP/G-31G(d,p) density functional level of theory? Thanks.
Helen
- 11
2
votes
0
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104
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Gaussian16 optical rotation calculation using a deuterated species
I am running into issues preparing an input file for DFT calculations. Currently, I am trying to submit an optical rotation calculation for an alpha-deuterated benzyl bromide (1 deuterium on the ...
2
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0
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38
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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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