What is Qm: Definition and 1000 Discussions

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. G

    QM prediction violating Bell’s inequality

    I have read many explanations of Bell’s proof that mention in passing something like “According to QM, the correlation between measurements of spin at different angles should be given by the cosine of the angle between them.” Sometimes they talk about 1-cos(x)/2. Sometimes they talk about...
  2. D

    Electric & magnetic field of a photon in QM

    Generally, all that matters is the amplitude of the wavefunction. You usually can't even MEASURE the phase unless you are making a particle interfere with itself. With photons, however, the real & complex components seem to appear as electric and magnetic fields. Is there anything equivalent...
  3. ShayanJ

    Confusion about position operator in QM

    In quantum mechanics, the position operator(for a single particle moving in one dimension) is defined as Q(\psi)(x)=x\psi(x) , with the domain D(Q)=\{\psi \epsilon L^2(\mathbb R) | Q\psi\epsilon L^2 (\mathbb R) \} . But this means no square-integrable function in the domain becomes...
  4. P

    Finding Beautiful QM Reads for Undergrad Exam

    I'm looking for good books to give me some more "taste" on beautiful aspects of QM. I'm actually studying for my undergraduate exam on the 27th november that comes in a strong academic flavour and would love a relaxed but deep reading. For example i totally loved Robbins's "What is...
  5. T

    Reconsidering Acceleration and Non-Inertial Frames in Quantum Field Theory

    When a changed body is accelerated in EM field, it is just a macroscopic net effect of multiple interactions of charged particles in that body with the other changed particles outside. When we say "particle accelerator", it is still a simplification, because particle is not being accelerated in...
  6. S

    [QM] Conservation probability to degenerate eigenvalues

    Hello =) I have a question regarding the conservation of probability in quantum mechanics. We know that the probability of a measurement of a given observable, is preserved in time if the observable commutes with the Hamiltonian. But this is also true if the value of the measurement...
  7. ORF

    In QM, can the trajectory in the phase-space split?

    Hello. I was told that "in QM the information doesn't disappear". Does it mean that, in QM, the trajectory in the phase-space can't split? [The typical example is a vertical simple pendulum, with the mass above the spin-point; in classical mechanics you can't know if the pendulum will fall one...
  8. G

    Quantum Teleportation - Misconceptions and QM fundamentals

    I'd like to go over what Quantum Teleportation is, how it works, and the absolute basic fundamentals of quantum mechanics. This thread may contain some relatively advanced concepts, but this is what I've learned over only a couple months. This only scratches the surface of the tip of the iceberg...
  9. T

    Why Does Functional F Not Yield Expected Results in Merzbacher QM Exercise 9.8?

    I think I almost get there, but something's not right, and need your help. if F(ψa,ψb) is a complex valued (scalar) functional of the two variable vectors ψa and ψb with linearity properties. Show that F can be represented as an inner product F(ψa,ψb)=(ψa, Aψb), for every ψa,ψb and the previous...
  10. moriheru

    RQM vs QM ( relativistic quantum mechanics vs quantum mechanics)

    What are the advantages of RQM against QM? If RQM is more accurate that QM then why use QM (yet only if it is) or better said if it is more complete? I read Paul Diracs lectures 1-4 and he talked about relativistic quantum mechanics and quantization of flat and curved spaces in lectures 3-4, so...
  11. R

    Determine the state |n> given results and probabilities [QM]

    Homework Statement In a spin-\frac{1}{2} system all particles are in the state |\psi\rangle. 3 experiments performed and are separate, the results are as follows: Particle in state |\psi\rangle, measured S_z = \frac{\hbar}{2}, with P=1/4 Particle in state |\psi\rangle, measured S_x =...
  12. K

    QM questions: MO theory orbital combination

    1) When we learn about MO theory, we learn that there are different ways to combine atomic orbitals to find the molecular orbitals for a molecule. However, going back to the fundamental/physical meaning of orbitals, orbitals are the wavefunctions. Wavefunctions do not have any physical meaning...
  13. Len hakureu

    Help for self education on QM & Theories on Time

    im planing to educate myself . on quantum mechanics/physics . so could you please refer me 1 good fundamental QM text / reference book . and 1 book that covers all the theories on time ( space time , time line ...)
  14. R

    Unit Circle and Quantum Predictions [hidden variable model agrees with QM?]

    I would like to reopen a discussion on assertions made by David Mermin such as: “There is no conceivable way to assign such instruction sets to the particles from one run to the next that can account for the fact that in all runs taken together, without regard to how the switches are set, the...
  15. Vannay

    Only took one upper-level QM course.

    I'm beginning the wondrous process of applying to graduate schools. Long story short in my last semester of undergrad stuffs I took Modern Optics instead of taking Quantum Mechanics II. Modern Optics is still a 400 level course but at the time I wasn't considering applying to physics graduate...
  16. jbrussell93

    Did anyone else strongly dislike QM?

    I'm a senior physics major in the first semester of a two semester QM sequence using Griffiths. All of the physics majors talk about how great quantum mechanics is and how it is the pinnacle of the undergrad physics degree. The upper level physics courses seem to build up the foundation that one...
  17. J

    QM and Determinism: Can We Predict the Future?

    "Determinism often is taken to mean causal determinism, which in physics is known as cause-and-effect. It is the concept that events within a given paradigm are bound by causality in such a way that any state (of an object or event) is completely determined by prior states" -- from wiki Does...
  18. T

    Please advise me on how to study Gottfried QM

    I am in a graduate class taught by a super genius who advises us to just keep rereading Gottfried (it's the sole text and all HW comes from it) if we don't understand. Me and my classmates feel like we aren't learning QM because the text is inscrutable and the HW isn't teaching us anything...
  19. N

    Quantum Mechanics & General Relativity: Explaining the Singularity

    I keep hearing that QM and GR don't play well together. For example, a singularity, a result of GR, is small enough for QM to apply but...it doesn't. I was hoping someone could explain exactly where the "equations fail." Unfortunately I'm so ignorant in this subject matter that I can't be...
  20. D

    Exploring Multi-Particle Quantum Mechanics with Falstad's QM1D Simulator

    http://www.falstad.com/qm1d/ is a really good way of getting a feel for the dynamics of a single particle in a variety of potential wells. Does anyone know of an equivalent (hopefully free) program for multi-particle systems? Dustin Soodak
  21. O

    Ideas for QM undergrad research project

    Hi everyone! I am an undergraduate student interested in quantum physics. I want to do a project in quantum but do not know how to come up with a good idea to start with. I have read the book Zettili and most of the book Cohn-Tannoudji. so I think I am able to work on a good idea. Any idea...
  22. L

    How an electromagnetic amplitude becomes QM probability?

    At the core of the quantum concept by Planck was the black-body radiation, then: electromagnetic waves, whose amplitudes are electric and magnetic fields, but when one follow the developments and one comes to the Schrödinger waves, now their amplitudes are not of that kind but related to...
  23. T

    Gauge Invariance in QM: P_y - Conserved or Not?

    I have a problem concerning gauge invariance in QM. QM should be invariant of electromagnetic gauge. However, the following two physically equivalent vector potential: 1. A = (-\frac{1}{2}By, \frac{1}{2}Bx, 0 ) 2. A = (-By, 0 , 0 ) generates the following hamitonian: 1. H =...
  24. EverGreen1231

    What Are the Best Books for Beginners in Quantum Mechanics?

    Hello, I'm taking a break from school this semester to work and pursue interests that I have let fall to the way-side due to studies. I'm an EE major but physics is sort of a "hobby" that I enjoy learning past what is required for my classes. I would like to take a QM course next year some...
  25. Omega0

    Susskind about QM - Reversed Time - Experiment?

    Hi, I had a look at Susskinds explanation about QM and this is pretty strange from my point of view. Video: Around minute 36. He says that if there is no measurement after the electron/photon/whatever is going trough the slit and if you would reverse time the whatever would come...
  26. B

    Understanding the Incompatibility of Discrete Space and Time with Relativity

    Relativity and continuum I have read contrasting things about the issue. Can you explain briefly why the assumption of discrete space and time is absolutely incompatible with relativity? What is the main problem? Lorenz invariance or what? Thanks
  27. T

    Brainfarting reading Griffiths QM (small step in solving Hydrogen atom

    I can tell this is simple, but I'm just not seeing it: (pages 146-147) Radial equation = d^{2}u/dp^{2} = [1 - p_{0}/p + l(l+1)/p^{2}]u Later... (having stripped off the asymptotic p^{l}e^{-p} parts) d^{2}u/dp^{2} = p^{l}e^{-p}{[-2l-2+p+l(l+1)/p]v + 2(l+1-p)dv/dp + p*d^{2}v/dp^{2}} And he...
  28. T

    Looking for a hard determinism type of QM interpretation

    Hi all! I am wondering if there is an interpretation of QM where the future is "set in stone" (for lack of a better phrase). It can be unknowable (the future)...but it shouldn't be random in any way. Edit: basically I'm looking for a hard determinism type of QM interpretation.
  29. Z

    Should I memorize all the derivations in QM?

    Hi. I'm a self-learner, and I'm doing an introductory QM from Griffiths. My question is should I memorize all the derivations and proofs in the book or I just have to memorize the final results? Another point is that I have nobody to ask about my solutions to problems or to help me in the hard...
  30. jedishrfu

    Revisiting an Old Interpretation of QM

    I found this article recently on Wired.com and thought others might like to see it. Basically its revisiting Bohmian Mechanics in the context of fluidics and how everyday objects can have quantum-like behavior explained via pilot waves: Fluid Experiments Support Deterministic...
  31. R

    Those Pictures (Representations) in QM and the density equations

    Hi there: I am reading a book (Atom-Photon interaction by Claude Cohen-Tannoudji, Page 448) and the following things gave a big headache. (1) Is there a density equation in Schrodinger Picture. because I encounter one, like: ##i \hbar \frac{d \sigma}{dt}=[\hat{H}, \sigma]## and...
  32. Avatrin

    QM - complement for Griffiths

    Hi I am currently trying to learn quantum physics using David J. Griffiths textbook. However, in chapter 4 and 5 he lost me a little. I would prefer a textbooks that handholds me through solving the PDE's rather than just giving me the solutions. The topic of these chapters are: QM in three...
  33. Q

    Is QM necessary for single observable parameters?

    Forgive the title if improper, the language of QM is not my native tongue. :) All scenarios where QM is invoked that I am used to involve parameters that do not commute, but I suppose I've never truly asked myself if QM is necessary to describe scenarios wherein you are not concerned with this...
  34. I

    Could the reason Gravity is not compatible with QM be

    because of the probabilities located in the equations of QM, wave functions and uncertainty principles? Instead of exact values for particles in QM there are potential ranges of values, these ranges over greater 'theoretic energy value difference' (like a range instead of an exact value of 5...
  35. I

    Why is theory of Gravity and QM incompatible?

    I am wondering why if quantum mechanics is self consistent, equal to itself, and thought to be equal to reality, and the same can be said of the theory of Gravity, why the separate theories and equations can not be plugged through a process of guess and check/trial and error by supercomputers...
  36. G

    Confusing integral (from a QM problem, of course)

    Homework Statement The mathematical complication I'm having comes from Problem 1.9 in Griffiths' Introduction to Quantum Mechanics. I'm just going to provide the mathematics here: The norm squared of the wave function is \ \left|\Psi \right|^{2} = (\frac{2am}{h\pi})^{1/2}...
  37. fluidistic

    Can the Operator n dot L Have the Same Eigenvalues as Lz in Quantum Mechanics?

    Homework Statement I've been told that the operator ##\hat n \cdot \hat {\vec L}## has the same eigenvalues as ##L_z##. Later I've been told that it has the same eigenvalues as any component of ##\hat {\vec L}##. But I am a bit confused, as far as I understand the eigenvalues of ##L_x##...
  38. S

    Solutions: QM Claude Cohen-Tannoudji

    Hey guys, I studied with this book now for some weeks. The last few days I solved a lot of exercises to prepare for the exam, but unfortunately I can not check if my answers are correct. There are no solutions in this book. Does anyone know if the solutions are availabe somewhere? This would be...
  39. L

    Books on Quantum Technology/ Applied QM

    Could anyone recommend an up-to-date and not too advanced book or online notes on applied quantum mechanics or quantum technology? Most of my books are quite old and I need to have a basic understanding of the subject for a work experience project in six weeks time. Thank you!
  40. T

    Educational Path to QM and QM Occupations

    Hi, my name is Tristan Barrow, I know this forum has gotten a lot of questions like this but none of them really fit my particular needs so I thought I would ask it again. Do the math subjects I am interested in lead me to Quantum Mechanics? If not what would be the best place for me given...
  41. B

    Mastering Landau QM: A Comprehensive Guide to Chapters 1 & 2

    Having done a course in QM I still find the first two chapters of Landau Vol. 3 extremely dense. Is there any nice reference that closely parallel's Landau's development, just giving more details/examples? Literally just the first two chapters, but done almost the exact same way + details/examples.
  42. ChrisVer

    Ehrenfest Theorem in Quantum Mechanics: Bohr-Sommerfield's Theory

    I read today about Ehrenfest's theorem on mechanical systems (with adiabatic hamiltonian evolution). Well in the book, it says that the Ehrenfest's theorem was also used by Bohr and Sommerfield who proposed the quantization of quantities such as: \oint p dq According to Bohr-Sommerfield's...
  43. binbagsss

    Clebcsh Gordan Coefficients - QM

    I'm looking at how a l j1,j2,jm> state can be operated on by the ladder operators, changing the value of m, and how this state can be expressed as a linear combination of l j1, j2, m1, m2> states. Where the following relationships must be obeyed (x2): m=m1+m2 l j1-j2 l ≤ j ≤ j1+j2 So...
  44. E

    On transmission coefficients in QM case -checking my reasoning

    Homework Statement The task is to calculate the transmission probability when E<V0 given that the step potential barrier is of infinite length. Homework Equations So far it seems simple enough. For region I, where x<0, (we're assuming, as usual, that the particles/ waves are coming...
  45. R

    Struggling with (I think pretty trivial) eigenfunction work for QM.

    This is the sort of thing that should be easy but my brain has blanked due to be overloaded in other areas of Physics. I've tried a great deal of different approaches but I'll walk though the one that led closest. I assumed that \hat{A} and \check{B} where both hermitian so there...
  46. samgrace

    Question about QM description of metallic conduction

    I have read in a classical EM book: " The picture of conduction electrons moving freely in conductors is an oversimplification, although it gives a good qualitative description of many of the properties of electric current. In some materials the current is due to the motion of carriers...
  47. DaTario

    QM and a new way to calculate probabilities

    Hi All, Would it be reasonable to state that, together with the quantum mechanics appearance, there appeared also a new way to calculate probabilities? I have never heard any teacher pointing out that QM has brought a new probability method. They speak of amplitudes of probability but...
  48. I

    Delta-function normalization (QM)

    I'm trying to understand what is the correct rule for the Dirac delta normalization of a non-integrable wave function, and can't seem to find any decent references. My issue is with achieving the proper dimensionality of the resulting wave function. This would be length-1/2 for the states of a...
  49. kq6up

    Best QM Textbook Recommendations for Self-Study

    I am starting to review to go back to grad school. One topic I didn't feel like I did so hot in as an undergrad is QM. I want to go through a textbook myself. I was thinking about "Principles of Quantum Mechanics, 2nd Edition" by Ravi Shankar. Are other books that might be good for me or...
  50. H

    Does QM violate the causality principle?

    Hello, As written, I am wondering if the causality principle gets violated in QM. Do virtual particles violate the causality principles? Do instantaneous events violate the causality principle? Thank you in advance.
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