Hello Edwin Obune.

You may had difficult to make an input of your model in Quantum ESPRESSO, right? Have you used QE before? How can I help you with this?

Best regards,

Ricardo Tadeu

Hello Ricardo, Just seeing your response. I'm a first time user. It has been difficult because I can't get any directive on the internet. I built my model using VESTA (2nm) GaAs. I will send you more info regarding my difficulties. In fact I needs help from the most fundamental of quantum dot input into Q.E to calculate the band structure. My email is [email protected]. I am grateful for your response. Edwin

Hello Edwin Obune

So, you modeled a 2 nanometer quantum dot of GaAs, right? I did the same to understand how it's done. About Quantum ESPRESSO, you must know some aspects first. It's a periodic plane wave code. This means that it requires that you create a "box" in which your system is modeled. You only define one "box" and QE makes this "box" interacts with the neighbor boxes. When you have periodic compounds, like oxides, crystals, etc., this simplifies a lot the calculation, because the code will only make the calculation of the unit cell, and kind of repeat to the other cells. Also, as much symmetric the system is, faster the calculation. The "problem" of Quantum ESPRESSO code is when you want to study an isolated system like a molecule, or in your case, a quantum dot. A quantum dot is a really small agglomerate of atoms, and we consider them to be "isolated" from each other.

How to model it in QE? You must model a very big box and put your system in the center. This box must be very big because your system must not interact with the neighbor systems. And then it makes the calculation really costly, because of the size of the box. In this file input of Quantum ESPRESSO I attached, a calculation would require more than 600 GB of RAM memory. This is needed to do a calculation of 167 atoms in the center of a box with 45 Angstrom of size.

So my question to you is: Do you really need to use DFT or Quantum ESPRESSO? Are you sure this is the best method and code for quantum dots? I never made calculations with quantum dots, but there are DFT codes like ORCA or Gaussian, which are not a periodic plane wave codes. And methods like semi empirical. So, you have to be sure what kind of model you can use.

Best regards,

RIcardo Tadeu

Thanks again Recardo. I presented your idea to my Academic Advisor and we are going to look into your idea and communicate back to you. We are going on break now and I will be doing this during the holiday break. Have a Merry Christmas and happy holiday in Brazil.

Cheers

Edwin Obune

You are welcome. Merry Christmas and happy holiday for you. I look forward to hear about your next steps.

Cheers

Ricardo Tadeu