четверг, 10 декабря 2015 г.

The practical use of quantum chemistry (my opinion)

The following is my private opinion, maybe not fully right.
The science can be divided into fundamental (or "pure") and applied branch. The applied science is funded well by business. The fundamental science, as I think, can be funded by the state only. The business should not fund an applied (or, for example, humanitarian) research, not because it is not useful, but because when a fundamental discovery is made, the profit of it is gained by everyone, not by those only who funded the investigation.
This picture illustrates the thesis, that the applied science is funded better than the theoretical:

So, the quantum chemistry is mostly a fundamental branch of science. Its applied use is quite limited (mostly, as far as I know, to the computations of the properties of small molecules in the gas phase). At the same time, quantum chemistry is relatively suitable for such “fundamental” tasks as, e.g., exploring the mechanism of a chemical reaction.
Such explorations usually do not have a significant applied use, but they can eventually give the opportunity to perform applied investigations – after decades. For example, if someone investigates a mechanism of a reaction, in a long time after that his conclusions can be used by experimentalists for applied investigations. So, the applied chemistry serves as a kind of “locomotive” for fundamental chemistry investigations. For humanitarian science, as I suppose, there is no such a “locomotive”, and because of that the humanitarian science is in a “mire” (as I think).
Figuratively speaking, applied chemistry usually answers the question "How much", while quantum chemistry answers the question "Why". This phrase is somewhat an exxageration; more clear explanation can be read here.
Performing quantum chemistry investigations for groups of experimentalists, I have found that quite often the theoretical and experimental methods give “different realities”, not intersecting each other. This means that if experimental methods are used, for example, to investigate a mechanism of a chemical reaction, or the dependence of experimentally obtained data on some structural properties of the molecules, these methods often lead to wrong conclusions. The quantum chemistry methods disprove these conclusions, but often do not give an alternative, because, as mentioned above, the quantum chemistry is of quite limited applied use. Maybe in the future these “realities” will intersect, and then the main method of investigations will be the combination of quantum chemistry with the experimental methods.
I have heard that the quantum chemistry has very low predictive power, and is mostly used to confirm experimental data. Again, this “predictive power” is something applied, while “confirming an experiment”, “understanding an experiment” is mainly the fundamental science.

The quantum chemistry is mainly efficient for investigating the gas phase and replaces some experimental methods like gas electron diffraction. And again, investigating the gas phase is often needed mostly in fundamental science – astrophysics, meteorology.

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