# Latest **URL:** https://forum.solidstate.quantumtinkerer.tudelft.nl/latest.md [Latest](https://forum.solidstate.quantumtinkerer.tudelft.nl/latest.md) · [Categories](https://forum.solidstate.quantumtinkerer.tudelft.nl/categories.md) · [Tags](https://forum.solidstate.quantumtinkerer.tudelft.nl/tags.md) --- ## [Welcome to the solid state physics forum](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/welcome-to-the-solid-state-physics-forum/7)
**Author:** [@system](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/system)\ **Replies:** 0\ **Last updated:** [August 14, 2020, 4:55pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/welcome-to-the-solid-state-physics-forum/7 "2020-08-14T16:55:49Z")
This is the place to discuss basic topics in solid state physics. While everyone is welcome to participate, the main use of this forum is the TU Delft TN2844 course “solid state physics”. The course materials are availa… --- ## [Exam grades](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/exam-grades/3867)
**Author:** [@r.t.debrouwer](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/r.t.debrouwer)\ **Replies:** 1\ **Last updated:** [June 8, 2026, 8:35am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/exam-grades/3867 "2026-06-08T08:35:57Z")
Is there any information on when we get the grades for the final exam? In respect to the fact we have the retake in 2 weeks and 2 days, meaning we have to make the choice for the retake soon. --- ## [2019 ex2 part d](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/2019-ex2-part-d/3843)
**Author:** [@m.f.h.dekoning](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/m.f.h.dekoning)\ **Replies:** 1\ **Last updated:** [May 19, 2026, 12:02pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/2019-ex2-part-d/3843 "2026-05-19T12:02:54Z")
Hi! I had a question regarding the answer. It asks when the diffraction peaks disappear and computes this straight from the form factor. However I tought that the peaks are peaks in intensity, and intensity varies with … --- ## [Exam 2025 Question 1c](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/exam-2025-question-1c/3841)
**Author:** [@rekhart](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/rekhart)\ **Replies:** 1\ **Last updated:** [May 19, 2026, 11:11am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/exam-2025-question-1c/3841 "2026-05-19T11:11:46Z")
Why is there a discontinuity in the DOS for the lower eigenvalue here? I don’t really understand what they say in the solutions about the 4 k points below E0 belonging to E- and above E0 belonging to both E- and E+… I… --- ## [Doping and devices ex. 2.3](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/doping-and-devices-ex-2-3/3840)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 19, 2026, 11:10am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/doping-and-devices-ex-2-3/3840 "2026-05-19T11:10:58Z")
they use n\_D ~N\_D, but if you use the expression for the concentration of n\_D, than you’d get something like: exp(something) = 0 due to the +1 in the Fermi-D distribution. Does this mean the exponent should go to -inf so… --- ## [2019 Ex3 part d](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/2019-ex3-part-d/3839)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 4\ **Last updated:** [May 19, 2026, 10:54am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/2019-ex3-part-d/3839 "2026-05-19T10:54:53Z")
Question:Why can’t I use the same approach as the free electron model in a semiconductor? I think I know the answer because at T–\>0 your electron density in the conduction bend goes to zero due to the fermi dirac dist… --- ## [Solutions of the minitests](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/solutions-of-the-minitests/3832)
**Author:** [@m.singh-9](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/m.singh-9)\ **Replies:** 1\ **Last updated:** [May 18, 2026, 12:50pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/solutions-of-the-minitests/3832 "2026-05-18T12:50:27Z")
Where can I find the solutions of minitests 1, 2 and 3? --- ## [Minitest 3 2026 exercise 1b](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/minitest-3-2026-exercise-1b/3830)
**Author:** [@j.a.leffers](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/j.a.leffers)\ **Replies:** 1\ **Last updated:** [May 18, 2026, 11:25am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/minitest-3-2026-exercise-1b/3830 "2026-05-18T11:25:51Z")
Hey, I had a question about this exercise. For this question you needed to sketch the reciprocal lattice and the first Brillouin zone. I didn’t know how to sketch it and in the answer (you can find in the picture) the… --- ## [Final Exam 2019 question 2](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/final-exam-2019-question-2/3805)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 6\ **Last updated:** [May 17, 2026, 5:00pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/final-exam-2019-question-2/3805 "2026-05-17T17:00:10Z")
Hey I have a question about this exercise. Based on how the axis is defined we can define the primmitive unit cell as the solutions suggest. My problem with this is that it is visible in the sketch that a basis of B(1… --- ## [Question about theory](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/question-about-theory/3826)
**Author:** [@r.t.debrouwer](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/r.t.debrouwer)\ **Replies:** 1\ **Last updated:** [May 17, 2026, 4:55pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/question-about-theory/3826 "2026-05-17T16:55:24Z")
I have seen this image multiple times already, but mainly without context about what it’s for. However I can guess that it’s used for calculating the amount of electron states in a material. Shouldn’t the factor 3 in … --- ## [Minitest 3 2019 exercise 2](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/minitest-3-2019-exercise-2/3827)
**Author:** [@DCBlom](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/DCBlom)\ **Replies:** 1\ **Last updated:** [May 17, 2026, 4:47pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/minitest-3-2019-exercise-2/3827 "2026-05-17T16:47:52Z")
I don’t see how the given potential generates the band structure we see in the solution. The potential is a Dirac delta train of 2 different alternating atoms, why does it have a band structure that would be the same for… --- ## [Nearly free electron model lecture](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/nearly-free-electron-model-lecture/3824)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 17, 2026, 11:53am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/nearly-free-electron-model-lecture/3824 "2026-05-17T11:53:44Z")
In this part, it is said that dk is the distance from the center, shouldn’t it be that dk = |k-pi/a| ? since if you don’t, then for k=0 the would become E0 -vhpi/a, just the same as the k’-part. --- ## [Band structures in 2D question 1.4](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/band-structures-in-2d-question-1-4/3825)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 17, 2026, 11:48am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/band-structures-in-2d-question-1-4/3825 "2026-05-17T11:48:11Z")
In the answer of the question it is said that the material has an even number of valence electrons, meaning it is an insulator, but this isn’t true right? when it is even it can still be all 3 possibilities right? --- ## [Many atoms per unit cell 1.1](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-1-1/3810)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 14, 2026, 7:52pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-1-1/3810 "2026-05-14T19:52:31Z")
I think it would really help when in the last part the |sin(ka/4)| part above, would be switched with the |cos(ka/4)| below since then it would correspond correctly with the + part and the - part of the equation before. … --- ## [Many atoms per unit cell question 2.7](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-question-2-7/3809)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 14, 2026, 6:53pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-question-2-7/3809 "2026-05-14T18:53:03Z")
In this excercise they expect you to know about Bloch’s theorem already according to the answers, because how else are you supposed to know that there arises another factor (-1)^n in the periodic eigenstate when k=pi/a? --- ## [Many atoms per unit cell question 1.6](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-question-1-6/3808)
**Author:** [@hajoW](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hajoW)\ **Replies:** 1\ **Last updated:** [May 14, 2026, 1:52pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-question-1-6/3808 "2026-05-14T13:52:29Z")
During the whole question it is really confusing which a is being used, it would help a lot if in the answers they would use an a0 and an a\_new term or something like that because in the answers they say ka = pi, but … --- ## [Ex3 Basic principles semiconductors](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/ex3-basic-principles-semiconductors/3802)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 1\ **Last updated:** [May 7, 2026, 9:42am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/ex3-basic-principles-semiconductors/3802 "2026-05-07T09:42:25Z")
I have a question about this exercise. I was making it and using the expression Eh=-E relating the electron energy and the hole energy of the same band. And the Hamilton equations for the group velocity and the effective… --- ## [Nearly free electron Ex3 part 1](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/nearly-free-electron-ex3-part-1/3801)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 2\ **Last updated:** [May 2, 2026, 11:36am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/nearly-free-electron-ex3-part-1/3801 "2026-05-02T11:36:57Z")
Hey I have a question. I was wondering why for exercise 3 and all the other homework exercises we don’t use similair methods discussed in the lectures and the reader. After looking a little deeper into the mathematics… --- ## [Where are the example minitest?](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/where-are-the-example-minitest/3797)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 2\ **Last updated:** [May 1, 2026, 8:38am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/where-are-the-example-minitest/3797 "2026-05-01T08:38:49Z")
Hey I have a question. During the whole course in this forum I haven’t had any sight of example minitest or example exams. While in a question I saw that someone does have acces to them leading to the conclusion that my … --- ## [Example Minitest 3, Question 1](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/example-minitest-3-question-1/3794)
**Author:** [@r.t.debrouwer](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/r.t.debrouwer)\ **Replies:** 2\ **Last updated:** [April 30, 2026, 1:52pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/example-minitest-3-question-1/3794 "2026-04-30T13:52:05Z")
In minitest 3 they ask to give the primitive lattice for the structure of boron and nitrogen. In the answer they take the boron atoms as lattice vectors, however I solved it using a middle point lattice like shown bel… --- ## [Many atoms Ex3 part 4](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-ex3-part-4/3783)
**Author:** [@khilversum](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/khilversum)\ **Replies:** 2\ **Last updated:** [April 25, 2026, 10:22am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-ex3-part-4/3783 "2026-04-25T10:22:20Z")
In the prior exercises we used a unit cell that looked like (K1,K2,K3) as this is the smallest repeating pattern. Now in part 4 we get a symmetric matrix and we make a symmetry argument \[1,1,1\]^T \[1,a,1\]^T \[1,a,-1\]^T … --- ## ['Many atoms per unit cell' Ex 1.2](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-ex-1-2/3782)
**Author:** [@c.a.martens](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/c.a.martens)\ **Replies:** 1\ **Last updated:** [April 21, 2026, 9:45pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/many-atoms-per-unit-cell-ex-1-2/3782 "2026-04-21T21:45:40Z")
In this exercise, we have the dispersion relation \\omega^2=\\frac{\\kappa}{\\mu}\\left(1 \\pm \\sqrt{1-\\frac{4 \\mu^2}{m\_1 m\_2} \\sin ^2\\left(\\frac{1}{2} k a\\right)}\\right) The answer states that the band gap is centered arou… --- ## [LCAO model Exercise 4](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/lcao-model-exercise-4/3753)
**Author:** [@c.a.martens](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/c.a.martens)\ **Replies:** 1\ **Last updated:** [April 7, 2026, 8:44pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/lcao-model-exercise-4/3753 "2026-04-07T20:44:46Z")
In part two of this exercise you are asked to calculate the new onsite energies of the two orbitals in presence of an electric field. In the answers they use that \\left\<1|\\hat{x}|1\\right\>=-d/2. Is there a trick to see th… --- ## [Debye model Exercise 3](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/debye-model-exercise-3/3733)
**Author:** [@c.a.martens](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/c.a.martens)\ **Replies:** 1\ **Last updated:** [March 25, 2026, 11:04pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/debye-model-exercise-3/3733 "2026-03-25T23:04:17Z")
In this exercise my initial thought was to split up the integral into a part for the transverse and parallel polarizations. When I checked the answers I noticed that the DOS is combined and a single \\omega\_D is used as u… --- ## [Interpretation vibrational energy states Debye model](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/interpretation-vibrational-energy-states-debye-model/3731)
**Author:** [@c.a.martens](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/c.a.martens)\ **Replies:** 1\ **Last updated:** [March 22, 2026, 9:18pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/interpretation-vibrational-energy-states-debye-model/3731 "2026-03-22T21:18:03Z")
Say we have N beads on a string along the x direction. The beads can only deviate from their equilibrium position in 1 dimension (say the y direction, transverse to x). Then there exist N normal modes in which the system… --- ## [Interpretation bosonic modes Einstein solid](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/interpretation-bosonic-modes-einstein-solid/3730)
**Author:** [@c.a.martens](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/c.a.martens)\ **Replies:** 4\ **Last updated:** [March 21, 2026, 7:05pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/interpretation-bosonic-modes-einstein-solid/3730 "2026-03-21T19:05:05Z")
In the lecture notes on the Einstein model there is the sentence: “This oscillator is a so-called bosonic mode: when its wave function is in the n-th excited state, we say that it contains n bosonic excitations.” How s… --- ## [Typo in Semiconductors/Basic Principles/Conduction section](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/typo-in-semiconductors-basic-principles-conduction-section/3678)
**Author:** [@CGutierrez](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/CGutierrez)\ **Replies:** 1\ **Last updated:** [December 2, 2025, 3:00pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/typo-in-semiconductors-basic-principles-conduction-section/3678 "2025-12-02T15:00:06Z")
Dear site organizers, Firstly, thank you for this site as I regularly use it in my Solid State Physics course. I came across a typographical error in the Semiconductors/Basic Principles/Conduction section in the senten… --- ## [Why does the density of states of a semiconductor show no asymptotic behaviour compared to other bands?](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/why-does-the-density-of-states-of-a-semiconductor-show-no-asymptotic-behaviour-compared-to-other-bands/3557)
**Author:** [@t.devries](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/t.devries)\ **Replies:** 3\ **Last updated:** [May 20, 2025, 9:30am UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/why-does-the-density-of-states-of-a-semiconductor-show-no-asymptotic-behaviour-compared-to-other-bands/3557 "2025-05-20T09:30:55Z")
When trying to construct the density of states for a semiconductor, I used the approach from the many atoms per unit cell lecture. For me this looks very similar to a semiconductor with two bands, but the semiconduc… --- ## [Proposal to add to the book: a (more expansive) Index](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/proposal-to-add-to-the-book-a-more-expansive-index/3552)
**Author:** [@vzinschitz](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/vzinschitz)\ **Replies:** 0\ **Last updated:** [May 19, 2025, 12:46pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/proposal-to-add-to-the-book-a-more-expansive-index/3552 "2025-05-19T12:46:31Z")
Just a disclaimer: This is more of an idea that would make it a bit easier (possibly?) to navigate the site, but is also not necessary and really just a “if you find yourself with some free time on your hands” kind of si… --- ## [Basis in different types of unit cels](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/basis-in-different-types-of-unit-cels/3543)
**Author:** [@hbemer](https://forum.solidstate.quantumtinkerer.tudelft.nl/u/hbemer)\ **Replies:** 3\ **Last updated:** [May 18, 2025, 5:33pm UTC](https://forum.solidstate.quantumtinkerer.tudelft.nl/t/basis-in-different-types-of-unit-cels/3543 "2025-05-18T17:33:08Z")
Hi, I was wondering if the basis for e.g. a FCC would change if you would construct this for a primitive cell or a conventional cell. I would say for a primitive it’s (0,0,0) but this is clearly not the case for the con… [Next page](https://forum.solidstate.quantumtinkerer.tudelft.nl/latest.md?page=1)