Messages

1

General Questions and Answers / Can we obtain U value theoritically in ATK?

« on: February 22, 2020, 01:03 »

Dear all,
           In this link:http://hjkgrp.mit.edu/content/calculating-hubbard-u#opennewwindow, the author has offered a method to obtain U value theoritically by calculating occupatiosn as a function of alpha. Can we realize it in atk (ver.2015)?

Best

2

General Questions and Answers / Re: Is transmission eigenstate normalized?

« on: April 27, 2019, 10:14 »

Thanks for your help. If transmission egenstate is normalzied, I have then have another question. As seen in Figure1 in the attachment, one transmission eigenstate looks delocalized and the other one looks localized around left electrode and central molecule. If delocalzied states can integrate to 1 over space, why the localzied one can intergrate to 1, either?  (two states with the same isovalue)

3

General Questions and Answers / Re: Is transmission eigenstate normalized?

« on: April 21, 2019, 15:16 »

can anyone help me?

4

General Questions and Answers / Must electron-phonon coupling (EPC) be used for photocurrent for indirect band?

« on: April 20, 2019, 05:19 »

Dear Quantumwise staffs,
           Recently I have read the paper Efficient First-Principles Calculation of Phonon-Assisted Photocurrent in Large-Scale Solar-Cell Devices
. It can be seen phonon plays an important role in calculating photocurrent for inderect energy gap materials. However, phonon calculation using DFT is pretty expensive and time-consuming. So I want to know if there is one material with small difference between direct gap and indirect gap (e.g. direct gap :0.42 eV, indirect gap: 0.38 eV), under low temperature condition (i.e. phonon effect is suppressed), is it reasonable to calculate photocurrent  not considering EPC? Does  the calculated photocurrent  mainly come from transition of electrons through direct gap?
          Best wishes

5

General Questions and Answers / Is transmission eigenstate normalized?

« on: April 18, 2019, 04:16 »

Dear Quantumwise staffs:
        I wanna know whether all transmission eigenstates calculated with certain energy E and kpoint k have been normalized?

6

General Questions and Answers / Re: Can I remove dielectric layer when calculating molecular junctions-based FET?

« on: April 1, 2019, 09:31 »

thanks for your kind help!

7

General Questions and Answers / Re: Can I remove dielectric layer when calculating molecular junctions-based FET?

« on: March 31, 2019, 16:05 »

so you think that it's ok to remove the dielectric layer if we just want to add a dieletric layer with relative permittivity ε_r=1？

8

General Questions and Answers / Can I remove dielectric layer when calculating molecular junctions-based FET?

« on: March 29, 2019, 04:39 »

Dear Quantumwise staffs:
        For field effect transistor configuration in ATK, it can be seen that dielectric layer (in general, SiO₂) need to be added between metallic layer and molecular junctions in tutorials. In tranditional MOSFET, e.g. n-type enhencement MOSFET, dielectric layer is used to avoid the transport of carriers from conductive channel to gate terminal. Can anyone please tell me what the dielectric layer takes effect in molecular junctions? Is it proper (reasonable) to remove the dielectric layer when I construct molecular junctions-based FET?
         Best wishes

9

General Questions and Answers / Re: How to cancell imaginary frequency when calculating dynamic matrix?

« on: December 3, 2018, 14:21 »

Thanks for your help. I will do as you suggested.     In addition, I am sure that I  use exactly the same potential as mentioned in the paper because the reference the paper provides (Fig.1)  completely coincides with the that in VNL (Fig.2)

10

General Questions and Answers / How to cancell imaginary frequency when calculating dynamic matrix?

« on: December 2, 2018, 02:22 »

Dear  Quantumwise staffs
            I use empirical force  to optimize gamma unitcell of graphyne nanosheet and calculate phonon band in ATK. However, the calculated band has a lot of imaginary frequency.  The  adopted empirical force is  Brenner, which has been used in previsou work (see Figure 1 in attachment, doi: 10.1103/PhysRevB.85.235436 ). I have tried a lot (improve  convergence criterion of force and strss on cell to 1e-05*eV/Ang and 1e-07*eV/Ang**3, respectively, or increase repeatition in dynamic matrix to (9,9,1), even  decrease  max_interaction_range to 5.0*Angstrom) to cancell imaginary frequency but can't make it. I hope anyone can kindly help me.
           The script is attached to bottom (gamma.py).
           Best wishes

11

General Questions and Answers / How does the constraints work when performing NEB?

« on: August 19, 2018, 18:24 »

Dear Quantumwise staffs
           Can I perform NEB for some atoms while fix the other atoms in a system (ATK 2015)? I noitce that there is a option named Constraints in NEB block but I don't understand how does it work. As we know, when performing NEB, the optimized initial geometry and the final geometry should be given in NEB block in VNL. Obviously, there a few differences in positions of atoms between the initial and the final structures.  How does ATK process transistion of atoms which are added to tag of Constraints-Fixed from the initial to the final structure?
            Beset wishes     

12

General Questions and Answers / The problem on calculating energy of hydrogen atom using LDA and GGA

« on: August 19, 2018, 17:28 »

Dear Quantumwise staffs,
          I notice that calculated energy of hydrogen atom rangs between 12-14 eV instead of exact 13.6 eV when using LDA or GGA. Exchange-Correlation Functional, basis sets and pseudo potential I use are as follow.
         GGA-FHI-Tight Tier1    -12.53 eV
         GGA-OMX-High    -14.33 eV
         LDA-FHI-Tight Tier1    -12.19 eV
         LDA-OMX-High    -13.96 eV
         Mesh cutoff I select is 200 hartree for these parameters. I wanna know what cases such deviation of calculated energy for hydrogen atom?  Is the limit of pseudo potential or other factors which result in such deviation?
         Yours

13

General Questions and Answers / Re: A question about transmission pathway

« on: July 4, 2018, 04:26 »

thanks for your help!

14

General Questions and Answers / Re: A question about transmission pathway

« on: July 2, 2018, 12:49 »

anyone helps me?

15

General Questions and Answers / Re: A question about transmission pathway

« on: June 29, 2018, 05:03 »

Dear Stradi,
           Thanks for your help. I have the last question: in transmission pathway, radius and cap radius  of arrow indicate size of scaled transmission. I wonder are such two radii proportional to the value of scaled transmission?  e.g. For one device, If scaled transmission=1, then radius of arrow=0.2. Does it mean that if  scaled transmission=0.5, the radius of arrow=0.1?
            Yours sincerely