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. S

    How is the QM prediction derived for Bell's tests?

    Question 1: how is the QM prediction (i.e. cosine curve, shown below) derived for Bell's tests? in layman' termss Question 2: while Malus's law, some physicists say, is not related to this cosine curve. Is there an indirect/lengthy way to connect the two...
  2. M

    What is the qm interpretation of moseley's law?

    moseley did experiments on various elements and showed that the frequency of the k-alpha emission was proportional to the square of the proton no. The formula is (z-1)^2 proportional to the square root of frequency, with the -1 thrown in for the screening effect. The bohr model can explain...
  3. S

    Does QM solve/resolve a few philosophical issues in Physics?

    QM seems something out of our everyday experience and to some it might seem unusual/weird/undeliverable/a hoax...yet... perhaps it actually solves some of the conundrums in classical physics Does QM solve/resolve a few philosophical issues in Physics? 1) Classical physics says that every event...
  4. ThomasT

    Conceptual underpinning(s) of the QM projection postulate

    The title says it. I would like to see what knowledgeable people at PF have to say about the QM projection postulate -- primarily understandings of the conceptual reasoning underlying it. But anything anyone has to say about it is welcomed, including opinions that it shouldn't be a part of the...
  5. R

    Is This Book Suitable for Beginners Struggling with Quantum Mechanics?

    I'm a little bewildered by my recent dive into QM. I don't really understand what's going on. I'm thinking maybe I should study some wave mechanics first before I try QM proper. I'm not really good at math. I make an enormous number of mistakes and I need to be constantly reminded of what to...
  6. T

    Exploring the EPR Paradox: QM and Locality

    Sorry, I have 2 doubts about the EPR paradox. 1) Just check out if I am ok: What EPR proposed was that QM suggest that if two entagled particles, for example photons, prepaired in some special way, get away from each other then: a) if we measure their x-spin then one particle will get the...
  7. D

    Why is GR and QM not compatible?

    You always hear that GR and QM aren't compatible, but I've never seen an explanation as to why. If I had to guess I would say it's more than quantum mechanics isn't compatible with GR than the other way around, but I really don't know where the conflicts are.
  8. Doofy

    In what sense is QM not understood ?

    In what sense is QM "not understood"? This is something that I've seen repeated many times, but I'm wondering how accurate it is. I mean, we've got this mathematical framework where we deal with vector spaces, eigenstates, superpositions, mixed states etc. that works to a high degree of...
  9. D

    Can 1014 atoms exhibit quantum superposition and interference?

    Is there a maximum size an object can have above which it won't follow the laws of quantum mechanics anymore? e.g. could the double slit experiment in theory work with macroscopic objects?
  10. S

    What are vector/tensors operators in QM or in general any vector space

    I am interested in knowing that in QM what vector/tensor operators are? In fact how do they differ from scalar operators?
  11. W

    Question on the probabilistic nature of QM

    Question on the "probabilistic" nature of QM I read very recently something that I interpreted as stating that certain quantum-mechanical phenomena are necessarily probability-based: for instance the exact path traversed by a photon/electron in the double-slit experiment. That's all well and...
  12. P

    Question: Early history of QM

    Many popularized accounts of the development of quantum theory generally go like this: • Maxwell shows that all electromagnetic radiation is a variant of one phenomenon. • Experimental results measuring black body radiation are inconsistent with the radiation theory as understood. • Planck...
  13. T

    Does cosmic censureship hypothesis avoid incompatibility with QM?

    My understanding of the main problem with adding gravity to quantum theory is that gravity is proportional to 1/distance squared. And so for particles that have no size (like electrons), their gravity is effectively infinite in a collision. Or in quantum terms, the equations don't converge on...
  14. J

    Does Hamilton's principle follow from the Feynman formulation of QM?

    Do you think Hamilton's principle from classical mechanics can be deduced from Feynman's path integral in quantum mechanics? (We get across this question in another discussion: https://www.physicsforums.com/showthread.php?t=609087&page=5) Of course, there is a loose connection, since...
  15. C

    Does ST provide causation to QM?

    I have a cursory understanding of QM which (as far as I know) fails to provide causation for certain events such as neutron decay and electron leaps to lower orbits. My understanding is that there is (currently) no know "cause" for these, and other, events - they simply happen. We cannot, for...
  16. nomadreid

    Which equations give nonsense in the intersection of QM and GR?

    One of the most frequent questions in this forum is why there is a contradiction between General Relativity and Quantum Mechanics. The most frequent answer is that, in high-energy conditions, some integrals diverge, giving nonsense. I could not find a mention of which integrals one is talking...
  17. G

    Lorentz transform of a scalar in QM

    If you Lorentz transform a scalar: U^{-1}(\Lambda)\phi(x)U(\Lambda)=\phi(\Lambda^{-1}x) If you now perform another Lorentz transform, would it it look like this: U^{-1}(\Lambda')U^{-1}(\Lambda)\phi(x)U(\Lambda)U(\Lambda')=\phi(\Lambda'^{-1}\Lambda^{-1}x) ? But isn't this wrong...
  18. J

    Is probability a fundamental aspect of quantum mechanics?

    I watched this video http://www.youtube.com/watch?v=aJ0FVez0FSc&list=UU_fHG6JygMd7oIvQ5S_cSIg&index=7&feature=plcp and the guy says that we don't know wether probability is a fundamental description of the particle or wether it is because of our lack of knowledge of the underlying system (ie as...
  19. N

    Finite difference method for even potential in QM

    Hello to everyone, while solving homework course Nanotechnology and Nanocomponents, I have encountered a problem in FD method that is applied in even potential. In my homework assignment it is explicitly said that it must be done only in x>0 part of the domain, where my problem starts with...
  20. V

    Is quantum chemistry more theory heavy compared to chemical engineering?

    I'm a chemical engineering major and I have to take one of these. Is QM more theory heavy or are they about the same in that regard? I am leaning more towards QM. my only exposure so far has been with the "modern physics" part of general physics
  21. R

    Understanding GR vs QM: Contradiction in Neil de Grasse Tyson's Explanation

    Which is more difficult to understand general relativity or Quantum Mechanics. Neil de Grasse Tyson basically straight-up contradicted himself in a docu on Einstein. In the beginning he said, GR is so complex that only a few people can understand it. At the end he said GR is simple, profound...
  22. S

    Advanced Quantum Mechanics Books Suggestions

    I have a good enough grasp of basics of QM at the level of Griffiths and Binney. Anyways, I want to start a more advanced book. I have my heart set at starting one of the following Dirac's "Principles of QM" John von Neumann's "Mathematical Foundations of QM" L. Ballentine's "QM: A Modern...
  23. K

    The time evolution operator (QM) Algebraic properties

    Homework Statement The hamiltonian for a given interaction is H=-\frac{\hbar \omega}{2} \hat{\sigma_y} where \sigma_y = \left( \begin{array}{cc} 0 & i \\ -i & 0 \end{array} \right) the pauli Y matrix Homework EquationsThe Attempt at a Solution So from the time dependant schrodinger...
  24. R

    Brushing up on calc to prepare for QM

    I make way too many mistakes in calc so I'm going to go back and brush up so as to prepare for the exciting moment when I finally start studying QM. I'm using the Thomas text on calc, it's contents are listed below. What sections do you think I should really master. Plus David Griffiths' book...
  25. D

    Best way to learn QM comprehensively

    I want to go about learning quantum mechanics in a way that I can learn it in detail eventually. And I was wondering if someone could give me some advice or advice for how they learn't it, should I start learning calculus and the mathematics needed for understanding it or get one of these...
  26. R

    Dirac formulation of QM, motivation for SE

    In Dirac's "The Principles of Quantum Mechanics", in chapter V on the equations of motion Dirac proceeds with a line of reasoning that is something along the following lines (I've modified it a bit to coincide with what's taught in the course I'm taking) 1. We assume that the motion...
  27. TrickyDicky

    QM only possible in flat space?

    I was trying to think of QM in the context of different possible spatial curvatures since the standard cosmology (FRW model) admits at least in principle that 3-space can have positive, negative or no curvature, even if the flat space is favored by the CMB WMAP-COBE observations etc, when I...
  28. E

    Arising of exp(-ipx) in QM in quantum field theory

    Wave functions and their exp(-ipx) are base of quantum mechanics and QFT. But how to derive them the most simply that we will understand why they are base of QM? It is interesting that Feynman in his book "QED: The Strange Theory of Light and Matter" very simplifies QED, but he did not give a...
  29. T

    Best Books on Quantum Mechanics (Undergrad Level)

    I'm looking for a good book on QM to study from (at the advanced undergrad level), but the caveat is that it must be concise. What do you recommend?
  30. B

    Optimizing Math Study for Quantum Mechanics and Beyond

    These are the contents of the books I'm going to be reading to prepare myself for Quantum Mechanics. I was wondering if there any chapters that are not really necessary to learn. For instance, in studying Calculus it seems unlikely to me that infinite series will every be useful, though I...
  31. LarryS

    Do the degrees of freedom change for particles in a relativistic system?

    Consider one particle traveling at a relativistic velocity in 3-space. Then the configuration space of the system consisting of that one particle would have 3 degrees of freedom – 1 particle times 3 dimensions. Because of its high energy, the particle decays into, say, 2 particles. Now the...
  32. A

    Would you be able to do MS in QM in this case?

    If your major is basically going to be mechanical engineering, but you take electives that have to do with physics.. would those electives help you do MS in Quantum mechanics easily?
  33. A

    GR or QM: which is more 'fundamental'?

    Which and why do you believe will turn out to be more 'fundamental' (in the sense that one will prove to be the foundation of a theory which goes beyond the SM, while the other will be explained away by it). Or maybe both, or neither?
  34. T

    Is there a difference between Many Worlds Interpretation and Relational QM?

    Whats the difference between Many Worlds Interpretation and Relational QM. Here is what I understand in few words: MWI: The whole universe system evolves with Schrodinger Equation without Quantum Collapse, but when a subsystem interacts with other subsystem, it seems like Quantum Collapse...
  35. A

    Direct products and direct sums in QM

    Dear forumers, I have a question about taking direct sums and products of state spaces in QM. Picture I have a state space that describes two (indistinguishable) particles which is a direct sum of two one-particles spaces: \epsilon_t = \epsilon_1 \oplus \epsilon_2 Furthermore, picture that...
  36. E

    What is an observer, defined by QM?

    Couple noob questions. 1.What is quantum mechanical definition of an observer? 2.Why is looking at the double slit experiment with your eyes while the electron goes through any different than a camera looking? Each one is looking, one can just see better. Is it the fact that the outcome...
  37. E

    Advanced undergrad/grad book for classical mechanics as macro limit of QM

    Hi folks. I'm wondering who does a good job of explaining this limit, preferably with a good set of examples. It doesn't need to be too basic, but it'd be nice if it went through the phase space stuff a little (I get the impression that my grad prof didn't do a great job with some details based...
  38. M

    Does Non-Commutativity Explain Quantum Mechanics' Core Principles?

    Hi, I am trying to get a few fundamental concepts sorted out in my mind associated with the maths of non-commutative operators and the physical implications on QM. As such, I am simply looking for confirmation, clarification or corrections to any of the following issues. One of the most...
  39. Q

    QM and Relativity: Can They Coexist in the Explanation of Gravity?

    In relativity, things like gravity are suppose to be time frame independent, i.e. even if time stopped they would still exist frozen as they did before since a gravitational field instantaneously correlates over the distance it covers. However, in the new standard model, forces like gravity are...
  40. AlexChandler

    Question about the use of group theory in QM

    I am currently in my second undergraduate quantum course and just finished studying the addition of angular momenta. I am also in my third abstract algebra course and am now covering product groups and group actions. In my QM book (griffiths) there was a reference made to group theory. it said "...
  41. J

    QM and Classical System Coupled

    Hi Consider a small system A which is described by quantum mechanics. A large system B is surrounding A and this large system is described by classical physics. What kind of interactions has the system B to the small qm system? Compared to B is A very small so I guess one can neglect...
  42. J

    Were There Ever Empirical Reasons to Bring Human Consciousness into QM?

    I'm wondering whether physicists in the 1930's ever had experimental reason to interpret, for example, Schrödinger's cat, as a true paradox (because of the role of a human observer). Why didn't they default to Bohr's interpretation, that an interaction with a geiger-counter, or any classically...
  43. A

    Breit equation/relativistic QM and simplifications

    Hello there, I was reading an article on wiki about the Breit equation: http://en.wikipedia.org/wiki/Breit_equation And I'm having a hard time understanding a few thing about this equation. The first thing is that, from what I can gather, the Breit Hamiltonian is basically a Dirac...
  44. N

    Exploring Time-Independent Force in QM

    Homework Statement Hi In QM we define the force operator F as (in the Heisenberg picture) F = \frac{1}{i\hbar}[p, H] + (d_t F)(t) What I can't understand is that usually (actually, always) we write F = \frac{1}{i\hbar}[p, H] and neglegt the last time derivative. How can we be so certain...
  45. W

    Time as Parameter in QM vs Coordinate in QFT

    According to Peterdonis in an old thread According to Matterwave in https://www.physicsforums.com/showthread.php?t=573589 msg #11: Peterdonis said Time is a parameter in non-relativistic QM while as a coordinate in relativistic QM/QFT. But Matterwave said parameter and coordinate has...
  46. N

    QM mechanics book for review and reference

    Hi, I'm looking for a QM mechanics book, which I could use for review and reference. I've took 3 QM courses, the first two was based on Cohen-tannoudji and Sakurai, and the third was about atoms and molecules etc. , although I haven't studied scattering theory and relativistic QM/QFT. (I took...
  47. V

    Place to learn mathematics of qm

    hello there, i need a place or a book where i can learn the mathematics of QM. I am having trouble with linear operators and matrix formulation. Like how do you represent an operator? How can one jump between operators and then back to matrix formulation. I NEED THE BASICS! Thanks!
  48. X

    Tough exponential integral (QM, Variational Principle)

    Homework Statement http://img4.imageshack.us/img4/224/32665300.png The Attempt at a Solution http://img684.imageshack.us/img684/2920/scan0003xo.jpg I've uploaded my work so far since its much faster than typing and I'm stuck on the last line trying to solve the integral. The first...
  49. S

    Is uncertainty inherent in QM?

    For example let's look at a single particle, double slit experiment: we know that the particle (photon/electron) will land up on one of the fringes. however it is commonly understood that we cannot predict which of the fringes will it land up on. one could argue that since there was...
  50. S

    The Mystery of Quantum Entanglement: Feynman's View on the Double Slit Pattern

    Feynman said that " [the double slit int. pattern contains] the only mystery in QM" was quantum entanglement not established (and bells theorem not postulated) then yet? or did Feynman believe that the explanation for the double slit (interference pattern) would also somehow explain...
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