Talk:Density of states

message: I regrouped together the topics of this Talk pages that seem to refer to the same topic in the Article, and used to be scattered all over. 
To improve readability of comments, I also 'blockquoted' relevant part of the text in two posts (from source clearly quoted from the Article; but was not easily evident what was quoted while reading talk pages before). 
It seems people who added the following comments didn't return here, but this Article needs work on. For now, I didn't dare to do more than edit the text in Talk pages. --Marjan Tomki SI (talk) 16:12, 14 April 2020 (UTC)
thread_title: Density of states

message: In general a DOS is an average over the space and time domains occupied by the system.
Average of what??? wave function of the system? 91.154.126.87 (talk) 15:34, 26 February 2013 (UTC)
thread_title:  Question to the writer of the section before Introduction. 

message: Unlike isolated systems, like atoms or molecules in gas phase, the density distributions are not discrete like a spectral density but continuous.
(1) Why would atoms and molecules in a gas phase have a discrete density of states? 
(2) Is the author of this sentence possibly using the notion of "isolated system" too narrowly, perhaps referring to systems that studied and named in the literature? Presumably any system can be made isolated by isolating it. 
(3) What is the opposite of an isolated system? A well-defined, thermodynamic model system connected to a heat bath? Or any not-isolated portion of any system?
89.217.0.204 (talk) 12:46, 6 February 2015 (UTC)
thread_title:  Hard to understand generalization 

message: I propose to start out with the more general definition of the density of states for a quantum system: 
\nu(E) = \sum_{n} \delta(E-E_n), 
where E_n are the energy levels (eigenvalues of the Hamiltonian) of the system. IMO this is much easier to understand, since the reader need only be familiar with the very basic properties of a quantum system.
Later in the article one can present the density of states for a crystalline system. Here one will need to introduce (or at least mention) reciprocal space and other topics that require familiarity with solid state physics.  —Preceding unsigned comment added by Havard.haugen (talk • contribs) 10:02, 14 January 2008 (UTC)
thread_title:  Too limited definition 

message: If I am wrong, one can define the DOS in in the following simple way: "the histogram of energy levels" or "histogram of the eigenenergies". I think that It is a good idea to put this simple definition in the beginning of the article. I can imagine this could help, for example, undergrad students grasp the main point of the DOS thing. Condmatstrel (talk) 21:17, 15 June 2011 (UTC)
thread_title:  Defining DOS as a histogram. 

message: This is what I found now. 
Generally, the density of states of matter is continuous. In isolated systems however, such as atoms or molecules in the gas phase, the density distribution is discrete, like a spectral density. Local variations, most often due to distortions of the original system, are often called local density of states (LDOS). 
The piece I 'bolded' still seems to be unclear in several ways(as also seen also from two opinions I now moved together). So:
# I am not sure what 'Generally' should mean in this context (in 'incarnation' cited above it might have meant 'taken as average for volume of interest or measure', but is really undefined). 
# Original author might have in mind that DOS is variable, when looked in detail, but was somehow taken just with average as represented for an aggregate previously (ten years ago possibly before tools were available or being used for detailed data to be acquired? - if so I would be interested in a link to a source with stry on how and why it was so) 
# I also can't see where I can check if the 'bolded' statement about  continuous and/or discrete of actual property of matter (not just of possibility of it being measured) can be checked if it is true or not. 
At that level of detail (quantum) I surely can't rely on my 'common sense of macro world', where we don't experience quanta effects (because our biological info systems do aggregation, averaging and so on, without most of us being aware of that). So I also can't rely on my (macro) common sense about probabilities in quanta world being continuous; I would like to see references to sources (could be in wikipedia) that statement is based on and - if possible - to be able to have it traced to the experiments) showing it to be so - or not to be so. 
So anybody knows who determined that (etc.)? --Marjan Tomki SI (talk) 16:12, 14 April 2020 (UTC)
thread_title:  Part of disputed piece of text has been changed since then 

message: I have added a simple sentence stating the connection of the density of states to entropy. Maybe someone more familiar with the condensed matter point of view can expand this. Jorgenumata (talk) 19:59, 16 February 2008 (UTC)
replies: text: It seems that this sentence didn't survive a large edit made recently.  Any discussion of this topic is incomplete without discussing entropy (from my viewpoint entropy is the only reason to even talk about the density of states).  Man It's So Loud In Here (talk) 19:32, 9 March 2008 (UTC)
thread_title:  Connection to entropy 

message: Can someone who knows a bit about this stuff add a section on how the density of states can be experimentally measured? Thanks 137.222.30.62 (talk) 16:44, 15 June 2010 (UTC)
thread_title: experimental measures

message: ...which makes me wonder if the text and figure were copied (possibly inappropriately) from another source, e.g. a textbook? Can someone include inline cites for that material?  —Preceding unsigned comment added by 128.163.128.193 (talk) 17:47, 22 July 2010 (UTC)
thread_title:  Figure 2 is the third figure 

message: In solid states physics k_F is commonly used as symbol for the fermi-wave-vector. This might lead to misunderstandings.
In the context of inter-atomic forces D is often used.
SolidStateDD (talk) 15:04, 10 March 2011 (UTC)
thread_title:  Dispersion relations 

message: There is always a way to calculate the DOS for systems with a complicated dispersion (esp. with multi band dispersions with non quadratic / linear relationships, by application of the formula:
$\rho(\omega)=\int\delta(\omega - \omega_k)$
with $\omega_k$ the $k$ dependant dispersion of the system of interest.  — Preceding unsigned comment added by 77.100.221.252 (talk) 22:50, 3 July 2011 (UTC)
thread_title:  General calculation of DOS 

message: The line says "Angular dependent calculations or measurements on a systems consisting of a single crystal of a compound, for example, are not anisotropic. " Should this not be "are anisotropic" or "are not isotropic"? I don't want to make changes without vetting them, but this seems clearly a typo.129.118.128.128 (talk) 18:27, 17 August 2011 (UTC)
thread_title:  symmetry and density of states 

message: This page has no explicit formulae for the DOS, even for simple particle in a box/surface/well/quantum dot. I would like to add this section with derivations similar to this page (http://britneyspears.ac/physics/dos/dos.htm). Would this be considered a useful addition?Larryisgood (talk) 13:31, 3 April 2013 (UTC)
thread_title:  No explicit formulae 

message: Reference to the microcanonical partition function is missing--Biggerj1 (talk) 22:14, 5 March 2014 (UTC)
thread_title:  Reference to the microcanonical partition function is missing 

message: I think the easiest definition of the density of (quantized) states by far,
: D(E) = \sum_{k} \delta(E - E(k))
is missing here. k is a stand-in for any indices you may need, e.g. k \rightarrow (\sigma, \vec k) for electrons. I like this one the best because a) it follows directly from the words "density of states" and b) by rewriting the sum as an integral and plugging in your dispersion relation, you arrive directly at the results given in the article by simply evaluating the integral. It might not be as pedagogical as the others but I think it should be somewhere in the article. --92.211.105.220 (talk) 21:50, 7 September 2016 (UTC)
thread_title:  Easiest definition missing? 

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thread_title:  External links modified 

message: The green line is not a product of the DOS and fermi-dirac distribution; the DOS function should be shifted so that its zero (both for holes and electrons) lines up with the zero of the product (green) function. 137.120.234.19 (talk) 14:51, 2 July 2017 (UTC)
thread_title:  Figure 4 gives a wrong graph 

message: I don't see anywhere in this page the fact that DOS is the number of allowed states per unit energy *per unit volume*. 
At the very beginning this fact is omitted: "the density of states (DOS) of a system describes the number of states per an interval of energy at each energy level available to be occupied." 
This is a fundamental part of the definition of the DOS and it appears to be missing.  — Preceding unsigned comment added by 70.68.81.41 (talk) 20:46, 22 January 2019 (UTC)
thread_title:  Missing the relation to volume? 

message: The section on "Optics and photonics" is confusing and incorrect. It relies on primary refs that are not properly summarized; I don't think they support the section either. The primary refs are very detailed studies, not summaries of the relation between local density of states and photonics.
I add a nag-tag to the section. Johnjbarton (talk) 15:14, 16 March 2024 (UTC)
thread_title:  "Optics and photonics" section needs secondary or textbook sources.