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It is often said that the molecule simulation for drug discovery will be one of the most important applications of Quantum Computing (QC).

As we all know that the entire process of new drug discovery is a long and costly process.

How critical is the molecule simulation in the entire process of new drug discovery?

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    $\begingroup$ I think the premise of your question is incorrect. Currently it is not really possible to simulate the molecules, so it is unsurprising that people don't simulate molecules to discover new drugs. A better question is if we could discover new drugs by simulating molecules, and how much easier quantum computers make it to simulate molecules. $\endgroup$ Nov 5, 2021 at 9:53
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    $\begingroup$ @MateusAraújo, what do you meant that "Currently it is not really possible to simulate the molecules,", entire field (and lots of people) are working on this, right ? $\endgroup$
    – david
    Nov 5, 2021 at 19:03

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"Is molecule simulation by quantum computing critical for drug discovery?"

No. Drug discovery is happening right now, without quantum computers large enough to do anything that a classical computer couldn't do decades ago. So quantum computing is not "critical" for it.

Currently, polynomial scaling methods like DFT are used to study candidates for pharmaceuticals, and some people even think that those calculations are overkill, though quantum chemists and quantum computing researchers (who try to make a living off of selling the importance of their research work) would say its underkill. The bottom line is that drug discovery was happening before DFT simulations became popular, and it's still happening now (without quantum computers).

So how would quantum computers help? For molecules in which the accuracy of classical algorithms like DFT, CCSD(T), etc., is not good enough, the hope is that quantum computers will be able to do more accurate calculations (for example at FCI level) with less cost than classical computers would need for such accurate calculations, but currently it's hard to imagine that happening any time soon because the sheer cost in terms of the number of logical qubits and auxiliary qubits for error correction seems beyond what we'll have in the next decade.

Keep in mind that we can currently do calculations with FCI-level accuracy in the important digits, for systems with dozens of electrons, on classical computers, but that level of accuracy is not seen as important enough so people instead simply use DFT and maybe CCSD(T), but it's just not seen as worth it to do FCI-level calculations for drug design. If quantum computers could do calculations with FCI-level accuracy for the price of DFT, then surely we would use them, but with DFT costing only $\mathcal{O}(N^3)$ for $N$ electrons, it's hard to imagine quantum computers becoming relevant in the 2020-2030 decade, unless there's a huge breakthrough in the technology (I think breakthroughs at the algorithm level won't be good enough).

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  • $\begingroup$ @MarkS I see your point, and a lot of people bring up this "discrete Fourier transform" vs "density functional theory" issue all the time, albeit erroneously. In the sentence "methods like DFT are used to study candidates for pharmaceuticals" there is no way that DFT could mean discrete Fourier transform. If the reader wants to understand, I think they ought to search DFT online and notice that Google gives (at least for me) two Wiki articles, the second being density functional theory. CCSD(T) doesn't need to be spelled out, and "FCI quantum" is sufficient for a Google search for that one. $\endgroup$ Dec 28, 2021 at 4:11
  • $\begingroup$ @MarkS Thanks. I figured that vote was from you because of the timing! And I appreciated it! You may be right that spelling out DFT would be helpful. I can't help but remember my professor when I was doing my PhD, telling me not to do things like that because it would be, in his words, "patronizing". I didn't agree with him at the time, and still don't, but I worry that spelling out that acronym might just be a lot more annoying to people on this site than it is helpful. Probably the benefits of spelling it outweigh the drawbacks, but I also think the vast majority of people here know the term $\endgroup$ Dec 28, 2021 at 4:32

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