Linked Questions

1
vote
0answers
37 views

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 ...
24
votes
5answers
27k views

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{...
25
votes
3answers
57k views

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 ...
34
votes
2answers
11k views

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 ...
17
votes
2answers
6k views

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 ...
26
votes
2answers
2k views

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 ...
19
votes
3answers
603 views

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, ...
14
votes
2answers
2k views

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 ...
12
votes
1answer
8k views

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 ...
11
votes
1answer
3k views

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 ...
12
votes
1answer
947 views

"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 ...
12
votes
2answers
662 views

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 ...
7
votes
1answer
3k views

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 ...
4
votes
1answer
1k views

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. ...
3
votes
1answer
958 views

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 ...

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