Qm Definition and 1000 Threads

The hybrid QM/MM (quantum mechanics/molecular mechanics) approach is a molecular simulation method that combines the strengths of ab initio QM calculations (accuracy) and MM (speed) approaches, thus allowing for the study of chemical processes in solution and in proteins. The QM/MM approach was introduced in the 1976 paper of Warshel and Levitt. They, along with Martin Karplus, won the 2013 Nobel Prize in Chemistry for "the development of multiscale models for complex chemical systems".

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  1. A

    Solving QM Problem: Fermi's Golden Rule & Transitional Probability

    Hello all, I would like some guidance on how to approach/solve the following QM problem. My thinking is that Fermi's Golden Rule would be used to find the transitional probability. I write down that the time-dependent wavefunction for the free particle is...
  2. Z

    B Which one is correct? (the Matrix or Wave formulation of QM)

    hello matrix and wave formulation of QM are equivalent theories i.e they yield the same results Which one is most frequentely used by professional scientists in solving real problems and why ?
  3. lekh2003

    Momentum of Electron in a Box (IB Physics QM)

    Here's the question ^ My first thought to solving this is to use Heisenberg's uncertainty principle. $$\Delta x \Delta p = \frac{h}{4\pi}$$ Now, we approximate ##\Delta x = \frac{L}{2}##. Then, plug and chug we end up with:$$p =\frac{h}{2\pi L}$$ I thought this was it, especially because this...
  4. shankk

    I Is the classical relation between energy and momentum valid in QM?

    Here we are talking about non-relativistic quantum physics. So we all know kinetic energy T = E - V = \frac{1}{2}mv^2 in classical physics. Here V is the potential energy of the particle and E is the total energy. Now what I am seeing is that this exact same relation is being used in quantum...
  5. B

    I Different reference frames in QM

    Hello! I am dealing with a problem of a 2 level system (an ion in my case) placed in a Penning trap. Basically the ion is moving inside the trap under the influence of the magnetic and electric field and I need to study its inner 2 level system (basically the lowest 2 energy states) while it is...
  6. U

    B Question about QM and Neuroscience

    I have one request, I hope you could answer it…. I saw this article that makes heavy assumptions based on Quantum Electrodynamics, like something like formation of an energy domain or sorts, and it connects it with brain activity which is super weird, I did ask a neuroscientist and he said he...
  7. berkeman

    Finding expectation value of two operators in a 3 state QM system

    A recent thread by @coolcantalope was accidentally deleted by a Mentor (I won't say which one...), so to restore it we had to use the cached version from Yahoo.com. Below are the posts and replies from that thread. The cached 2-page thread can be found by searching on the thread title, and is...
  8. F

    I Does mean velocity equal group velocity of wave packets in QM?

    Does mean velocity of particle equal group velocity of wave packet in QM?If they do not equal which of them is classical velocity?
  9. W

    I Interesting Scientific American article (The end of QM?)

    https://www.scientificamerican.com/article/new-views-of-quantum-jumps-challenge-core-tenets-of-physics/?fbclid=IwAR0z2pTmGqTBkm2JzvSNe6piKPZCGbhdpyZWcHeLO_2B-w5fPxFRKgfrGvY I love quantum physics almost mystical and paradoxical nature. That seems to be ending. Especially with the advent of...
  10. entropy1

    I Determinism and causality in QM - a case

    I hope my thread won't be closed (too soon) and some forummers can shed their light over my question. Let's suppose a deterministic universe. I assume all events have a cause, that everything is cause and effect. Then, given that the state of the universe at some instant is X, and this leads to...
  11. S

    I What is the QM description of a macroscopic event?

    In classical probability theory, a probability space has a set of "point" or "outcomes" which may be multidimensional vectors. "Events" are sets of these points. By analogy, in QM, it seems a macroscopic event would defined (in principle and mathematically) by as a set of possible...
  12. J

    I Is completeness synonymous with hidden variables in QM?

    In one of the Insights. Either QM is incomplete (because we only have access to probabilities in conventional experiment) or there are Many Worlds. I want to pick incompleteness. But in Einstein context of it. Incompleteness means there were hidden variables. Is there another meaning of...
  13. entropy1

    B Will brain-computer interfaces reveal more about QM?

    Will brain-computer interfaces that are hooked up to quantum measurement devices reveal more about quantum mechanics?
  14. Morbert

    Using the QM Formalism To Make Predictions

    [Moderator's note: Thread spun off from previous discussion as it is more technical.] Adding to this: the formalism of QM is quite flexible when it comes to applying the projection postulate. We can even apply it before the time of measurement. Consider a preparation (at time ##t_0##) of a...
  15. I

    Expectation Value Notation in Griffiths QM Textbook Third Edition

    In the 3rd edition of the Introduction to Quantum Mechanics textbook by Griffiths, he normally does the notation of the expectation value as <x> for example. But, in Chapter 3 when he derives the uncertainity principle, he keeps the operator notation in the expectation value. See the pasted...
  16. thaiqi

    Quantum Nelson's Stochastic Interpretation of QM: Which Material is Best?

    Hello,everyone. Which material is best for Nelson's stochastic interpretation of quantum mechanics?
  17. H

    B Is there a probability in QM that an event happens at time t?

    Hi PF, A(x,t) is the probability amplitude at time t that a particle is at x. If it was emitted at (0,0) the propagator gives its value. I wonder if QM can give the amplitude of time probability B(y,t) that an impact will occur (for a given y) at any t. consider a screen behind the two slits, it...
  18. P

    Verifying that the uncertainty is 0 for a QM state

    By definition , ##\ket{+x} = \alpha \ket{+z} + \beta \ket{-z}.## Therefore we proceed , \begin{align*} \langle S_{x} \rangle &= \lvert \alpha \rvert^{2} \left(\frac{\hbar}{2}\right) + \lvert \beta\rvert^{2} \left(-\frac{\hbar}{2}\right) = (\alpha^{2} - \beta^{2})\left(\frac{\hbar}{2}\right).\\...
  19. F

    Does this QM experiment show that science is doomed?

    Here is the article: https://www.sciencemagazinedigital.org/sciencemagazine/21_august_2020/MobilePagedArticle.action?articleId=1611119#articleId1611119 If 2 experimenters (or people) cannot agree on a single observation does this mean that science which depends on many observers agreeing on...
  20. solklar

    Quantum Could you finish a course in QM (using Griffiths) with another book?

    Hello! I was wondering if there'd be any problems using another QM book (like Shankar, Ballentine etc) in a course where the standard literature is Griffiths Introduction to Quantum Mechanics? By that I mean is there ever any disadvantages to going to a more advanced textbook (assuming you...
  21. G

    Wavefunctions everywhere in Quantum Mechanics

    In QM, matter is made of standing waves (The postulate of QM and the Schrödinger Equations). The momentum of matter is related to the wavenumber (de Broglie wave). The electromagnetic waves are the traveling waves (Electrical Engineering). Can we expand the hierarchy of waves to the vacuum - a...
  22. AndreasC

    Help with 3-D interactive QM visualisation of a hydrogen atom

    First of all, I got to decide what I'm going to use to make the simulation. I know Fortran, Matlab etc but I'm pretty sure these won't help me much. I learned some C++ a couple years ago but my knowledge is rusty, however I think I'm going to use that combined with Unreal Engine, since it makes...
  23. Demystifier

    I Teaching Bohmian QM before standard QM

    In many physics curricula, some elements of the so called "old" (Bohr-Sommerfeld) QM are taught before teaching the actual QM. The pedagogic value of such teaching may be doubtful, but for someone without prior knowledge of QM, the old QM is more intuitive than the actual QM. That's because the...
  24. Lynch101

    I Anti-realist Interpretations of QM

    Having discussed interpretations of QM here and elsewhere, to only a basic level, I have encountered proponents of what is described as "anti-realism". This is not to be confused with "non-realism", which might be equated with simple instrumentalism or "shut up and calculate". To try and...
  25. K

    Does Summation Over n from -∞ to +∞ in Quantum Mechanics Equal Ψ(x)?

    I have a (trivial) question regarding summation notation in Quantum mechanics. Does ∑cnexp(iknx) = Ψ(x) imply that n ranges from -∞ to +∞ (i.e. all possible combinations of n)? i.e. n ∞ ∑exp(iknx) -∞ I believe it does to be consistent with the Fourier series in terms of complex exponentials...
  26. bhobba

    I Confusion Abounds In Discussing QM

    Hi All Have a look at the following discussion about QM: Its long so I do not expect too many people to watch it in its entirety. But it does show confusion about QM even amongst educated people, and the physicist involved IMHO seemed a bit 'confused' himself. You can easily see how the...
  27. U

    A The Penrose gravity thesis/interpretation of QM

    The Penrose interpretation postulates that the wave function is real and that there is objective collapse without departing from reality as we know it. It does not make any assumptions; the observations of quantum mechanics and classical mechanics are exactly what they appear to us. "Accepting...
  28. K

    I Spontaneous symmetry breaking from a QM perspective

    Hello! This questions might not make sense and I am sorry if that is the case (I am asking from a QM class perspective). I am a bit confused about the idea of spontaneously symmetry breaking (SSB), from the point of view of QM. I am talking here about the energy plot looking like a mexican hat...
  29. bhobba

    I Is the Following How Most Students Think of Einstein's View Of QM

    I was over on another forum discussing what Einstein thought of QM - namely he thought QM correct - but incomplete. His viewed changed a bit over time, but that was his final view. Anyway here is the reply I got: No serious Physicist (including all of my professors) thinks he was right. It's...
  30. entropy1

    Study Quantum Mechanics: Recommended Literature

    Hello, I want to try studying QM. I have already read Susskind Minimum QM. Now I have some trouble focussing while reading and mild dyslexia. So I only want to read the stuff I need (doesn't everyone?). HOW do I find the right sequence of the right books to progress from basic to more...
  31. Lynch101

    I Understanding the Fundamental Difference in Interpretations of QM

    I was originally going to start a thread on individual interpretations of quantum mechanics to try to understand them better, but after reading this article by @PeterDonis it might make more sense to use that as a starting point and try to understand how the different interpretations fit into...
  32. E

    A Question about the perception of collapse in relational to QM interpretation

    I'm diving into the RQM and one thing still puzzles me. I have hard time understanding this: Taking the model system discussed above, if O′ has full information on the S+O system, it will know the Hamiltonians of both S and O, including the interaction Hamiltonian. Thus, the system will evolve...
  33. entropy1

    I QM & Ontology: Why Should We Stay Away?

    I was thinking that QM and QM practicioners tend to stay away from the ontology part of QM, and see the QM framework as useful for predicting measurement outcomes. But if I see the properties of wood or plastic, they are explained by the properties of the particles they are "made up from", and I...
  34. entropy1

    B How much math is required to do QM?

    I write this post because there are some people that get irritated by my posts. I get why you do. I think the signal I am getting in several threads of mine, is that you could try to understand QM through interpretations, but that the prerequisite is that you then also have to understand the...
  35. E

    B Mapping between rules of classical vs QM probability?

    Apologies in advance for my ignorance, I don't really have a reference to consult and Google hasn't been too helpful! In standard probability theory there are a few common useful formulae, e.g. for two events ##S## and ##T## $$P(S\cup T) = P(S) + P(T) - P(S\cap T)$$ $$P(S \cap T) = P(S) \times...
  36. obstinatus

    I (Baby QM) Analytic Solution to the Infinite Square Well Problem

    Hi, I think I'm having a bit of a brain fart...I'm messing with this numerical code trying to understand the 1-D time-independent Schrodinger's equation infinite square well problem (V(x) infinite at the boundaries, 0 everywhere else). If normalized Phi squared is the probability of finding...
  37. I

    (QM) Number of states with Energy less than E

    Hi, so I'm having trouble with a homework problem where it asks me to find the number of states with an energy less than some given E. From this, I was able to work out the energy E to be $$ E = \frac{\hbar^2}{2m} \frac{\pi^2}{a^2} \left( n_x^2 + n_y^2 + n_z^2 \right) $$ and...
  38. Q

    Action of the time reversal operator on the QM wave equation

    Applying the time reversal operator to the plane wave equation: Ψ = exp [i (kx - Et)] T[Ψ ] = T{exp [i (kx - Et)]} = exp [i (kx + Et)] This looks straightforward as I have simply applied the 'relevant equation' however my doubt is in relation to the possible action of operator T on the i...
  39. Killtech

    I Can the hydrodynamic formulation of QM be understood purely classically?

    I was wondering this question for quite some time because this view seems to work surprisingly well and also coincides with how the state space must be setup in any attempt model QM within classical probability theory. So starting with the hydrodynamic formulation from...
  40. C

    I Definition of a Degenerate Subspace (QM)

    I was learning about Degenerate Perturbation Theory and I encountered the term 'Degenerate Subspace', I didn't really understand what it meant so I came here to ask - what does it mean? will it matter if i'll say 'Degenerate space' instead of 'Degenerate Subspace'? and subspace of what? (...
  41. Q

    B We can't unite QM with GR because of what the Qfield is capable of

    I think it can do more than the wave only events we know of (superposition, entanglement, and tunneling). If the quantum field doesn't care about spatial distance, does that mean every unobserved quantum wave is already everywhere throughout the quantum field? Does it explain spooky action at a...
  42. S

    A Algorithmic information theory's QM view of reality

    Where can I learn more about this conception of reality?
  43. SEYED2001

    A How effective can QM be to understand the mind and/or consciousness?

    I am very interested in the philosophy and science of the mind, as well as consciousness in neuroscience. I am also very interested in QM. Now, I wonder how QM can be potentially connected to my two previous interests on the consciousness and mind. I would also appreciate any reference to...
  44. SEYED2001

    What is the best QM textbook for me?

    Summary:: I am a last year high school student. I haven't chosed physics for my course, but I am very interested in QM, because I believe it act lik a gateway to the meaning of existence, and so the nature of mind, my particular interest. I want to know which textbook is the best for me. I am...
  45. bhobba

    B Interesting Book On The History Of QM And Einstein's Role

    Check it out: https://www.amazon.com/dp/B07PYMLZWJ/?tag=pfamazon01-20 Its available free if you have Kindle Unlimited. Many books do not get right that Einstein knew QM very well indeed and greatly admired Dirac, of whom he said: 'Dirac, to whom, in my opinion, we owe the most perfect...
  46. F

    I QM through stochastic optimization on spacetimes

    I have a simple question as a layman in the field: Is this worth reading, and even more, is it a contribution to possibly shorten the endless discussions in this subforum? https://www.nature.com/articles/s41598-019-56357-3.pdf
  47. TTT

    Nuclear Space in QM: Exploring & Integrating Finite Solutions

    If I understand this question correctly, I am supposed to prove an integrate from negative infinity to infinity ∫x|∅(x)|2(1+|x|)ndx is finite. Sorry, but I have no idea.
  48. A

    I Interpretations of QM vs. statistical physics as an "interpretation"?

    Personally I tend to believe all (or almost all) of the interpretations of QM are unsatisfactory simply because they tell us something that we already know but do not tell us something we don't know. That is, they do not predict new phenomena or principles or properties of matter, etc. that can...
  49. C

    I Question regarding a Free particle and Hilbert space (QM)

    In quantum mechanics, the Eigenfunction resulting from the Hamiltonian of a free particle in 1D system is $$ \phi = \frac{e^{ikx} }{\sqrt{2\pi} } $$ We know that a function $$ f(x) $$ belongs to Hilbert space if it satisfies $$ \int_{-\infty}^{+\infty} |f(x)|^2 dx < \infty $$ But since the...
  50. Lynch101

    I How is realism understood in QM?

    It seems that with every discussion I engage in, new thoughts and questions about QM keep popping up. I'm sure this is pretty standard but I hope that my questions haven't crossed the line into being excessive. I know that in the EPR paper the authors set out a criterion that, if fulfilled...
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