New answers tagged theoretical-chemistry
9
Predictabilty is essentially determined by the level of detail you need in your model to make a reliable prediction. Models that require little detail to capture the phenomenon of interest typically can give reliable predictions, while those requiring enormous detail typically cannot.
This is true for all the sciences—biology, chemistry, physics, and ...
13
Let me contribute two more reasons which make Chemistry hard to analyse from a purely theoretical standpoint.
The first one is that, viewed very abstractly, Chemistry essentially relies on the study of geometry in very high-dimensional spaces, and even from a purely mathematical point this can be extremely difficult. An important part of Chemistry is bond ...
8
"it seems that every other STEM field has models to predict results (physics, thermodynamics, fluid mechanics, probability, etc) but chemistry is the outlier"
This is only partially true, but there are areas of all of those fields where predictive power is difficult in practice due to the complexity of the system and convolution of features. In ...
18
Parts of chemistry have predictability but the combinatorial complexity of what is possible leaves a large amount of space for things that don't follow the rules
Some of the ways chemistry differ from physics in unpredictability are an illusion. Take gravity, for example. There is a strong rule–sometimes described as a law–that all objects near the surface ...
22
First of all, I'd ask: what do you admit as "chemistry"? You mentioned thermodynamics as being a field where you have "models to predict results". But thermodynamics is extremely important in chemistry; it's not right to classify it solely as being physics. There is a large amount of chemistry that can be predicted very well from first ...
1
Few people continue to investigate this issue, but it was an active field of research in Bohr's days. Bohr himself basically sidelined the question with a postulate of stability, and quantum mechanics avoided it altogether by postulating that the classical laws of physics do not hold on the atomic scale.
In the course the 20th century, successive generations ...
0
Yes, to re-iterate the above answer, CI in its standard truncation schemes (CISD, CISDT, etc.) are nowadays out of use in favor of CC for 3 main reasons:
(1) CC's size extensivity, and if the reference is separable, size-consitency
(2) CC exhibits the most rapid convergence to full CI
(3) CC's insensitivity to choice and quality reference due to inclusion of ...
1
I agree with the statement that FCI has no spin contamination, however, it's not necessarily true that if one reference is closer to FCI than other, it has less spin contamination (which is why UHF can produce better energies but lose spin symmetry). One way to think about it is by using the Thouless Theorem to relate any two non-orthogonal references
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