This is Eric's logbook for Nano Japan project from 2012.6.3-2012.7.27.
updated 2012.6.1 by Nugraha
Daily schedule†
- 09:00-10:00 Discussion (1)
- 10:00-12:00 Solve the problem and write the progress on pukiwiki
- 12:00-13:30 Lunch
- 13:30-14:30 Discussion (2)
- 14:30-16:30 Solve the problem and write the progress on pukiwiki
- 16:30-17:30 e-mail report and problems
Goal of the project.†
- Consider the time evolution of a special vibration (radial breathing mode RBM) of a single wall carbon nanotube after applying the local force at t=0 whose functional shape is a Gaussian in the real space. The time evolution is given by differential equations and solution should be given by animation gif generated by Povray and Giam software. (by R. Saito 2012.5.18)
- Keywords: Coherent phonon, radial breathing mode, carbon nanotubes, Differential equation, Fourier Transform, Povray and Giam, Mathematica
Schedule for discussion†
| Time and Day | Mon | Tue | Wed | Thu | Fri |
| 09:00-10:00 | Sato | Nugraha | Tapsanit | Tatsumi | Nugraha |
| 13:30-14:30 | Saito | Simon | Hasdeo | Simon | Tapsanit |
- Please note that:
All appointment should be done by communicating each other on what kind of subjects will you teach.
- If Eric-san asks you what he needs, please answer it with CC to Saito.
- If you do not have any materials to be taught, please give him an easy question to solve.
- If Eric-san could not answer this question, it means that your question is bad (needs some knowledge).
- If Eric-san can answer within 2 mins, it means that you gave improper question (the answer is too trivial).
Questions and Answers†
- This section is for posting questions from Eric-san and answers from other group members.
- Please list here with some simple reasons or details.
- For every problem, give a tag double asterisks (**) in the code so that it will appear in the table of contents.
- For the answer, give a tag triple asterisks (***) in the code below the problem in order to make a proper alignment.
- List from new to old.
Q: About Brillouin Zone†
Hey guys! So I believe this is where I should post questions. I don't have any specific questions today, but was just trying to understand Brillouin zones and Bloch's theorem, which appear a lot in Saito-sensei's book on Carbon Nanotubes.
From google I have an ok idea of what Brillouin zones are, but am still trying to figure out how they relate to the energy gap of the cell such as on page 28 of the CN book. I was also wondering how on page 47 the Brillouin zone can be a long line segment instead of a polygon.
If anybody has any quick words of advice for how to understand Bloch's theorem that would be great as well! It's a little bit intimidating and I'm not sure if there's a simple way to begin to understand it.
Thanks so much and see you guys in a couple of weeks!
Eric
Answer (by Tapsanit)†
Please consider my answers one by one in order to understand the Brillouin zone.
- What is the Bloch'theorem written in page. 17 of Saito's book?
- A: The electron in solid can behave as wave and its wave function which is denoted by &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; should satisfy the Bloch's theorem due to the periodicity of the atoms in solid. &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; is sometimes called the Bloch wave function. It can be written as the phase factor &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; times the periodic function in real space &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;, i.e., &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;; &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;. It is recommended to check that &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; satisfies the Bloch's theorem.
- What is the Brillouin zone? (solved in the discussion)
- A: We must understand the reciprocal lattice before answering this question, because the Brillouin zone is defined from the reciprocal lattice.
- What is the reciprocal lattice that define the Brillouin zone?
- A: As mentioned above, the electron in solid is a kind of wave whose wave function satisfies the Bloch's theorem. This means that it has the wavevector with amplitude and direction just like normal wave. The dimension of wavevector is 1/[length] which is a reciprocal of length in real lattice. Then, reciprocal lattice is constructed to obtain the wavevector of the electron. Please note that there are many wavevectors possibly obtained from the reciprocal space. The unit vectors of the reciprocal lattice &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; are obtained from the unit vectors of the real lattice &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; by following relations (&tex(): Error! cURL: Could not resolve host: chart.apis.google.com; denotes dot product of two vectors):
&tex(): Error! cURL: Could not resolve host: chart.apis.google.com;, where &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; if &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; and &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; if &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;.
It is recommended to try using this relations by deriving the unit vectors of reciprocal lattice, &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; and &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;, of graphene in Eq. (2.23) of Saito-sensei's book using &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; and &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; in Eq. (2.22).
Q: About copy machine†
Can I use a copy machine or printer?
A: (not solved)†
Yes, and they are across the hall from my room.
Q: About library†
I would like to know where the library is and how to use it.
A: (not solved)†
The library is on the 7th floor. To check out a book I write information on a special wooden card and place it where the book had been. I also give the slip inside of the book to the librarian, and I return the book to the librarian.
Report†
This part is basically written by Eric-san. Any other people can add this.
Here the information should be from new to old so that we do not need to scroll.
Task from Tapsanit (Bloch's theorem and reciprocal lattice)†
- Check that the &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; satisfies the Bloch's theorem.
- Answer:
Bloch's theorem is:
\[
T_{\vec a_i}\Psi = e^{(i\vec{k}\cdot\vec{a_i})}\Psi
\]
Here &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; is a translation operator: &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;.
Then, also note that &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; is a periodic function. We have &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; because &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; is a unit lattice vector. Thus:
\[
T_{\vec{a}_i} \Psi(\vec{r}) = \Psi(\vec{r} + \vec{a}_i)
\]
\[
= e^{(i\vec{k} \cdot (\vec{r} + \vec{a}_i))} u(\vec{r} + \vec{a}_i)
\]
\[
= e^{i\vec{k} \cdot \vec{a}_i} [e^{i\vec{k}\cdot \vec{r}} u(\vec{r})]
\]
\[
=e^{i\vec{k} \cdot \vec{a}_i}\Psi\left(\vec{r}\light)
\]
The Bloch theorem is satisfied.
- Derive the unit vectors of reciprocal lattice, &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; and &tex(): Error! cURL: Could not resolve host: chart.apis.google.com;, of graphene in Eq. (2.23) of CN book using &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; and &tex(): Error! cURL: Could not resolve host: chart.apis.google.com; in Eq. (2.22).
- Answer: Here we use
\[ \vec{a}_i = {\rm unit~vector~of~real~lattice} \]
\[ \vec{b}_i = {\rm unit~vector~of~reciprocal~lattice} \]
\[ \vec{a}_i\cdot\vec{b}_i = 2\pi \]
\[ \vec{a}_i\cdot\vec{b}_j = 0 \quad {\rm if} \quad i \neq j \]
From Eq. (2.22) of CN book:
\[
\vec {a}_1 = \left(\frac{\sqrt{3}}{2}a,\frac{a}{2}\right), \quad
\vec {a}_2 = \left(\frac{\sqrt{3}}{2}a,-\frac{a}{2}\right)
\]
\[ \vec{a}_1\cdot\vec{b}_1 = a_{1x}b_{1x}+a_{2x}b_{2x}=b_{2x}\frac{a\sqrt{3}}{2}+b_{2y}\frac{a}{2}=2\pi
\]
\[ \vec{a}_2\cdot\vec{b}_1 = a_{2x}b_{1x}+a_{2x}b_{2x}=b_{2x}\frac{a\sqrt{3}}{2}-b_{2y}\frac{a}{2}=0
\]
a ?_1=(?3/2 a,a/2), a ?_2=(?3/2 a,(-a)/2)
a ?_1?b ?_1=a_1x b_1x+a_1y b_1y=b_1x (a?3)/2+b_1y a/2=2?
a ?_2?b ?_1= a_2x b_1x+a_2y b_1y=b_1x (a?3)/2-b_1y a/2=0
?b_1y a/2 = b_1x (a?3)/2
?b_1x (a?3)/2+b_1x (a?3)/2=2?
?b_1x=2?/(a?3) ? ?-b_1y a/2=0 ? b_1y=2?/a
b_1=(2?/(a?3),2?/a)
Same process gives: b_2=(2?/(a?3),(-2?)/a)
I will fix this as soon as possible!
June 5 (Hasdeo teaches XX and YY. from 9:00-9:30) etc†
- Nugraha-san explained the problem of an infitie 1D series of masses connected by springs. We solved for the value of w^2, although there was a small error in my calculation. In excel we graphed the value of w^2 as a function of k, the wavevector. In the afternoon we graphed the (incorrect) data generated in excel into an xmgrace graph. Nugraha-san also explained how to use the simpler SciDAVis software.
Also, Florian-san showed me how to use the POV-Ray software. We installed it on the desktop machine and I worked through the basic tutorial.
- The homework is: by friday complete a graph of w(k) for the 1D phonon problem, determine the max/min for each branch, and interpret this physically. Which branch is optical and which is acoustic?
Also, solve the diff eq for a Gaussian.
If I have time consider the infinite 1D series of spring mass problems, but in the case that all masses are the same, but the spring constants are different.
June 4†
to do:
- Solve the same diff eq for f(t)=Ae^(-t^2/a^2)
- Clean up the solution for the reciprocal lattice from last week
![[PukiWiki]](image/c60.png "[PukiWiki]")
