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. U

    Quantum Math prerequisites for QM by David Griffiths

    What math should a person know to THOROUGHLY understand everything in this textbook(Introduction to Quantum Mechanics by David Griffiths)? (For refrence) cal2 cal3 diffeq1(ode) diffeq2(pde) linealg vectorcalc realanal1 realanal2 Please list all you think are necessary. Thanks
  2. X

    Studying Quantum Field Theory without taking graduate QM?

    Hello over the summer I would like to study quantum field theory. I took two semesters of undergraduate quantum mechanics using Griffith's textbook. We covered the entire book in those two semesters. I also know my special relativity pretty well. Is that enough to self study quantum field theory...
  3. zonde

    QM laws fundamental vs effective

    I have impression that physicists consider QM laws as fundamental, meaning that there should be a way how QM mathematical form is realized in reality. On the other hand QM laws could be effective laws resulting from some process of evolution. In that case it should be possible to characterize...
  4. D

    QM linear algebra true or false

    Apologies if this should be in homework section but I thought it best suited here. Been revising past papers but with no solutions. the following questions all require just a true or false answer. Any help or confirmation of my answers would be appreciated. 1 - every N x N matrix has N...
  5. J

    Exploring Voltage in Magnetic Fields: The Role of Quantum Mechanics

    Say you take an open circuited loop (not connected back to itself) and measure its voltage relative to some external reference point. Then you start rotating this loop in a magnetic field. Depending on the power of your motor, the loop will continue to spin for a finite amount of time. After...
  6. M

    Self-Study Graduate Quantum Theory with Sakurai: Lecture Notes and Resources

    Hello science buddies, This is my first post in this forum. Ok let me get to the point directly, currently I self-study graduate level quantum theory and the main book I'm using is Sakurai's. But I think for self studying it's better to also have a look at lecture notes, first because it's much...
  7. Ahmad Kishki

    The Mathematical Structure of QM and the Stern Gerlach

    Many books in QM (eg: Sakurai) mention that the stern-gerlach experiment provides enough motivation for the mathematical structure of QM, Sakurai even mentions Gottfried's book. Point is, i didnt find Gottfried's book, so i am looking for other books that develop the math of quantum mechanics...
  8. U

    Quantum Math requirements of QM by J. J. Sakurai?

    What math should a person know to THOROUGHLY understand everything in this textbook(J. J Sakurai. Modern Quantum Mechanics)? (For refrence) cal2 cal3 diffeq1(ode) diffeq2(pde) linealg vectorcalc realanal1 realanal2
  9. L

    Understanding Spacetime in QM and QFT: Time Treatment and Particle Tracking

    spacetime is classical and continuous.. so when quantum system form superposition or entanglement, how is time treated esp in qft? how does spacetime keep track of the particles of fields? or how does the fields or particles able to jump in spacetime.. how is this handle in qm or qft?
  10. Ahmad Kishki

    Linear algebra done right for qm

    I am trying to learn the formalism of qm, so i am following the book linear algebra done right but is it worth it to study every proof? I mean what is the attitude to follow with such a proof oriented book to eventually have a solid basis in the libear algebra of qm?
  11. W

    QM: Work done due a time dependent perturbation

    Homework Statement A quantum particle of mass ##m## is bound in the ground state of the one-dimensional parabolic potential well ##\frac{K_0x^2}{2}## until time ##t=0##. Between time moments of ##t=0## and ##t=T## the stiffness of the spring is ramped-up as ##K(t) = K_0...
  12. M

    Initial development of set theory and determinism in QM

    I am considering the following question and I want you to agree (but perhaps you don’t):Rutherford wrote a letter to Bohr, as an answer to a previous letter from Bohr containing one of the first of Bohr’s descriptions of the atomic model, saying that he understood the atom model Bohr advocated...
  13. H

    What is the meaning of current in QM?

    Consider a piece of conductor which is under a DC bias. Solving time-independent Schrodinger equation we have electron wave function which is time-independent and shows special probability for being in each position of the system. How can one say about transmission of electron from one point to...
  14. L

    Qm virtual particle force on wire, acrose the universe

    What would be the virtual particle force acting on a wire, which go's from say Earth to any part of the universe reseeding away from us at near light speed, or grater ?, would it break, and how would we compute it ? Lachlan
  15. 1

    Sources to learn QM while commuting to school?

    i go to school, and it's quite far away (3 hours per day, return), so, i'd like to use this time wisely and learn QM, but unfortunately, i can't read books on transportation, i get dizzy... when i read things for prolong period of time.. i've only learned about the special relativity, and am...
  16. S

    A question about QM "Observer effect"

    So if we "look" at a particle, then its wave function collapses. Does "look" mean, hitting that particle with another particle (a light particle?). A simple Yes/No answers first please. I mean, does its wave function collapse because we first need to hit that particle with an electron or a...
  17. snatchingthepi

    Griffiths QM 6.22: Deriving $E_{fs}^1$ from H$_r$ and H$_{so}$

    Homework Statement Starting from E^1_{fs} = \left<n l m_l m_s| (H_r + H_{so})| n l m_l m_s \right> and using E_r^1 = -\frac{(E_n)^2}{2mc^2}\left[\frac{4n}{l+1/2} - 3\right] and H_{so} = \frac{e^2}{8\pi\epsilon_0}\frac{S\cdot L}{m^2c^2r^3} and \left<\frac{1}{r^3}\right> =...
  18. Y

    Best textbook or video or device for understanding QM

    As the title says I am looking for some book to read and understand this world. I know many people say its impossible and that we can learn it by learning the math bluh bluh.. But i have passed 4 quantum courses and i know the math. I just can't get the touchable concepts ( i don't really know...
  19. S

    How does quantum mechanics explain the stability of macroobjects?

    Hi guys, I'm a newbie in this area of physics and like many other unfamiliar territories, I've had anxiety and confusion when I first heard the intriguing concepts of this theory. I hope someone can help me understand it better though it is evident that it's very difficult and...
  20. FadeToBen

    Expectation value of total energy in QM

    Homework Statement The problem asks me to find the expectation value of W. Homework Equations The given ψ[x,t] is Asin(πx/a) e^((-i Eot)/ħ). By QM postulate 2 the QM operator of W is: iħ δ/δt or equivalently -ħ/i δ/δt. The Attempt at a Solution <w>=∫ψ*iħδ/δtψ= iħδ/δt 1/(2e^(-iEot/)ħ)...
  21. Q

    Evidence for retrocausal interpretation of QM?

    This article about a recent experiment was just published the other day: http://phys.org/news/2015-02-hindsight-foresight-accurately-quantum-state.html I can't help but think that this is at least weak evidence in favour of the retrocausal interpretation. Of course other interpretations aren't...
  22. Ahmad Kishki

    Perturbation theory in qm self study

    i am currently self studying qm, and i am trying to plan ahead since i am relatively over with griffiths part1 (which is the theory part) and i was wondering if i should go ahead to part 2 (applications) or should i just keep this for later and attempt to stregnthen my basics in qm from another...
  23. J

    Beginner to QM with some questions

    1. Is there any reason to interpret the wave function as probabilities of specific states rather than an actual interference of those states? Or are there some types of measurements that are better thought of as probabilities? For example, thinking of the particle as a point-like object with the...
  24. TrickyDicky

    Localization of states and elementary vs composite in QM

    While browsing Wikipedia I bumped into this sentence that seemed partially wrong to me but maybe I didn't understand what it is referring to so would like for some expert to help me elucidate it: "Even if an elementary particle has a delocalized wavepacket, the wavepacket is in fact a quantum...
  25. Ahmad Kishki

    Quantum Discovering an Unknown Quantum Mechanics Book: An Unconventional QM Journey

    https://www.amazon.com/dp/9384007447/?tag=pfamazon01-20 I cannot find any reviews for this book, yet i found in a nearby library literally hundreds of copies.. So anyone heard of the author or that publisher med tec? I actually bought it and i found it quite easy but radically different from...
  26. S

    Tricky Integral from Griffiths QM

    Homework Statement ##\int_0^\pi \sin^{2l+1}\theta~d\theta## Homework EquationsThe Attempt at a Solution I have no idea how to proceed with integrals of this type, and I can't find any similar examples online. If someone could give me some info on these types of integral, or direct me towards...
  27. M

    John Wheeler & QM: Unpacking His Interpretation of Quantum Mechanics

    Does anyone know how Wheeler understood QM? Here are some well-known sayings of his (slightly paraphrased): "the wave function does not represent the electron- it represents what we know about the electron; the joint product of all the evidence that is available to those who communicate" "it is...
  28. ShayanJ

    Quantum What are some recommended books for understanding the mathematics of QM?

    I want to read a book on mathematics behind QM and by that, I don't mean just functional analysis. Its been a long time that I hear about things like *-algebra, C*-algebra, Weyl algebra, Heisenberg group, Stone-von Neumann theorem and things like these and I want to understand them. Can anyone...
  29. Coffee_

    [QM] Addition of spin for normal and identical particles

    1. Problem: Consider the composed system of two particles of spin ##s=1## where their angular momenta is ##l=0##. What values can the total spin take if they identical? What changes when they are distinguishable? The Attempt at a Solution : The problem I have here is incorporating the fact...
  30. Coffee_

    QM, the convergence of the harmonic oscillator function.

    1. After finding out that the wave function ##\Psi(z) \sim Ae^{\frac{-z^{2}}{2}}## in the limit of plus or minus infinity Griffiths separates the function into two parts ##\Psi(z)=h(z)e^{\frac{-z^{2}}{2}}## My question will be about a certain aspect of the function ##h(z)## After solving the...
  31. M

    Will mastering QM benefit future EE/CE professionals?

    Hello, I recently read that MIT redesigned its EECS program. It redesigned it about 30 years ago to include more mathematics and solid-state physics but this time they are adding more QM. At my university, we study basic QM in freshman year physics and then again in third year in an EE subject...
  32. S

    System with two particles with spin QM

    Homework Statement Two particles with spin ##S_1=1## and ##S_2=1## are in our system. For wavefunction of the first particle we know that ##S_{1z}|\psi _1>=\hbar |\psi _1>## while for the second particle ##S_{2x}|\psi _2>=\hbar |\psi _2>##. a) Find wavefunction ##|\psi _1>## in basis with...
  33. LarryS

    Probability Postulate in Relativistic QM?

    In non-relativistic QM, the probability postulate works very well in position and momentum space. But, I have read that in relativistic QM (Dirac or QFT), the probability postulate in position space does not work because the corresponding probability density function is not Lorentz covariant...
  34. Coffee_

    [Intro QM] A bit confused on spin of system notation

    1. In Griffiths, in the section where he discusses the 'total' spin of two spin 1/2 particles (''Addition of angular momenta'') he starts of using a notation new to me. Namely ##\chi=\chi_1\chi_2## where I know what ##\chi_1## and ##\chi_2## represent independently, which has been discussed in...
  35. T

    Time in QM vs SR: Energy, Frequency & Motion

    In QM, the energy operator is proportional to the time derivative E ~ d/dt So higher energy particles have higher frequencies, i.e. their wave functions change more often per time than when at rest But in SR, higher energy particles seem to exist in slow motion, appearing to age little How...
  36. R

    Does Quantum Mechanics Necessitate Consciousness?

    There is soooo much misinformation out there that for the non-physicist, it is difficult to know whether to trust one source or not. So, one thing I do not understand is, based on what I've read, how QM does or does not require consciousness. It seems a debate that has been going on almost...
  37. D

    Quantum How will you rate the QM book of Stephen Gasiorowicz?

    Can anybody tell me about the book 'Quantum Physics' by Stephen Gasiorowicz? You can give some comparison with other books such as Griffiths or Shankar's QM book.
  38. A

    Engineering QM Books for Engineers: Best Intermediate Picks

    Hey guys, I love to read and learn about Quantum Physics and have been looking for good suggestions on books. I don't want a complete beginners book, I am an Electrical Engineer so I have a decent background in math and physics, by no means am I am expert. I love all the theory behind QM but...
  39. Amaterasu21

    Question about time in QM vs. special relativity?

    This question is about both quantum mechanics and special relativity, so I wasn't sure which forum to post it in. If mods think it's in the wrong forum then please move it as you see fit! My understanding is that in special relativity, we live in a four-dimensional "block universe" of...
  40. N

    Realism in QM: Existing Before Measurement?

    I think it's the idea that things exist even before we measure them, correct?
  41. B

    Can Bob & Alice disagree on QM description of experiment?

    Let's say Bob and Alice are passing through a lab on their way to lunch. In the center of the lab is a big table with some kind of experimental set up. They are curious about it and both silently examine the whole thing (there is an unrelated lecture going on nearby so they are silent and...
  42. T

    Is there a difference between Emergence & QM Amplification?

    I recently read the published article: Stuart Hameroff, How quantum brain biology can rescue conscious free will. Front Integr Neurosci. 2012; 6: 93. PMCID: PMC3470100 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3470100/ From this it seems that current neuroscience views consciousness as an...
  43. A

    What is the purpose of the analogies and equations used in the QM TV program?

    Hi I was watching a TV program about QM on BBC4 given by Jim Khalili. I am a little confused by two aspects. First, he attempted to draw an analogy about polarisation of entangled particles always being opposite when measured, by using a card game where a dealer deals cards in pairs. I think it...
  44. S

    QM & Speed of Light: A Random Thinking

    Just to clarify: I only have very rudimentary knowledge of Physics, so please correct me if I am wrong. This thought came to my mind after I discovered some youtube videos and articles on the double slit experiment: AFAIK, if the information of which path the electron takes is obtained, there...
  45. E

    A (relatively) simple QM Problem, but seeking my mistake

    Homework Statement Find <r> and <r2> for an electron in the ground state of hydrogen. Express in terms of Bohr radius. Homework Equations We know the relevant wave functions are: R_{10} = \frac{c_0}{a}e^{r/a}Y^0_0 and Y^0_0 = \frac{1}{\sqrt{4\pi}} The Attempt at a Solution As I...
  46. B

    How do we get from quantum mechanics to statistical mechanics?

    Hey guys, I'd like to ignore Hamiltonian mechanics and use a specific example of the many particle Schrodinger equation in Griffith's chapter 5.4 to try to get to statistical mechanics, and see what happens, I need help making sense of it: Given 3 non-interacting particles in a 1-d potential...
  47. dextercioby

    Dirac's QM - First Edition 1930 - 2 pages needed

    Hi everyone, so I need someone to go to a public library and 'steal' somehow (scanning or simply photo with a smart phone) pages 34 and 56 of Dirac's original edition of his groundbreaking 1930 book called <The Principles of Quantum Mechanics>. I myself cannot do that from where I am, not to...
  48. R

    Quick question about integrating limits in QM problems

    Am I correct in assuming that if there is a potential present and it is not infinite then integrals will always be made from minus infinity to infinity, but where an infinite potential exists then the integral will depend on the size of the confinement area? Sorry to be a little disambiguous...
  49. H

    QFT & QM: Spinors, NRQM & Dirac Field Explained

    Often I see QFT texts introduce dirac spinors by comparing them to the two component spin states (which I have come to accept are also spinors) in NRQM. And arguing that since the NRQM spinors transform via SU(2), our desired quantum fields for spin 1/2 particles should be some higher...
  50. S

    QM - free particle in one dimensional dpace

    Homework Statement A particle in one dimensional space, $$H=\frac{p^2}{2m}$$ in time ##t=0## has a wavefunction $$ \psi (x)=\left\{\begin{matrix} \sqrt{\frac{15}{8a}}(1-(\frac{2x}{a})^2) &,|x|<\frac a 2 \\ 0 & , |x|>\frac a 2 \end{matrix}\right.$$ a) Calculate the expected values of ##x##...
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