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Topics - wot19920302

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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 / 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

3
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?

4
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

5
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

6
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     

7
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

8
General Questions and Answers / A question about transmission pathway
« on: June 19, 2018, 09:26 »
Dear Qunantumwise Staffs:
         In VNL, threshold in transmission pathway is described as "only include scaled tranmission above the given threshold. The transmission t are scaled as (t/tmax)**ρ, where ρ is the scaling power."  So scaled transmission tscale= (t/tmax)**ρ. I notice that the default  ρ is 0.00. What does it mean? Let's take the example,  if  local bond transmission between atom A and atom B  t=0.4,  the tmax=1, when default  ρ is 0.00, the scaled transmission   tscale= (t/tmax)**ρ=(0.4/1)**0=1.  That's to say, for all transmission pathway,   when  ρ is 0.00, tscale always equals to 1 and the threshold doesn't make sense in that case. Should I set ρ=1.00?   In addition, from the definition of scaled transmission, the radius of arrow seems the relative value ( (t/tmax)). Does it mean that I can't compare conductance of two different devices? 

9
General Questions and Answers / a unexpected tranmission dip at fermi level
« on: April 1, 2018, 09:15 »
Dear Quantumwise staffs:
            I construct a device using (4,4) carbon nanotube(CNT) as electrodes connecting to carbon atoms chains and calculate transmission spectra. (Mesh-cutoff I select is 100 hatree and k-point is 1*1*100. The functional is spindependent GGA-PBE). However,  there are sharp transmission dips at fermi level  whether bias voltages are applied nor not .  It's well kown that (4.4) CNT is metallic and there is no bandgap around fermi level.  I can't figure out why there are unexpected dips in transmission spectra, can anyone help me? :o
           Best
          P.S  Fig.1 is calculated transmission specta at 0V, and Fig.2 is contact types of device I construct.

10
General Questions and Answers / Can ATK calculate optical properties of system?
« on: February 1, 2018, 14:15 »
Dear Quantumwise staffs:
           One of my colleague wanna know can ATK calculate optical properties such as adsorption wavelength, emission wavelength, etc. I can find there is "opticalspectrum" in analysis term for bulk configuration. I don't know whether it is  what he wants. Do you have tutorial about how to calculate optical properties?
           Best

11
General Questions and Answers / Can we optimize a portion of atoms along certain directions in ATK.2015?
« on: December 8, 2017, 10:46 »
Dear Quantumwise staffs:
           Should we optimize the part of atoms in the system along the certain direction in ATK.2015?  For example: there are 5 atoms in the system, numbered by 1, 2, 3, 4, 5.  I just want t o relax atom 1, 2  along the x, y direction and keep z fixed. Other atoms also keep fixed.  How do I do that?
Best

12
General Questions and Answers / why is my density of states not smooth？
« on: October 15, 2017, 13:57 »
    Dear scholars, I have a question about ATK (ver.2015). Now I want to look at the hybrid configuration at spinterface between BDT molecule and Nickle. And I used slab model to simulate interface, which is subjected to present conditions. The trouble matter is as follows:
When I calculate density of state of BDT contacting on Nickle, the image is not smooth.
    I used builder to build its slab model, and then I optimized the bulk and added the analysis of density of state to script.Please look at script1.And follow this I calculate its density of state, but the result is not good. The image of DOS is not smooth prospectively. Please look at image1. I try many methods to change this situation, trying to increase k-polint sampling to 9*9*1, increasing vacuum size to 20, I just hope the DOS of energy-independece image be smooth. However I didn’t find the real reason to avoid this. What good method could solve this trouble?Being more smooth by this slab simulating?
      Best
 

13
General Questions and Answers / How does ATK obtain charge distribution on individual atom in *.out file?
« on: September 8, 2017, 14:46 »
Dear Quantumwise staffs：
          When we finish scf, we can get *.out file that reports charge distribution on every atom like figure1 (rectangled by black lines). I wonder how does ATK justice which electron belong to which atom? Are these distribution the same with  Mulliken population or not? Can I use these data to calculate net magnetic moment?  :-\
Best

14
General Questions and Answers / Differences between electron density calculating using DZP and SZP
« on: June 10, 2017, 05:14 »
Dear Quantumwise staffs:
        I calculated spin density of one system using SZP and DZP (ATK ver.2015) and found the difference exists in left and right edges. Fig1 is spin density using SZP, Fig2 using DZP. I can't understand what leads to such results. Could you please help me?
       Best
       Attachments are scripts. script1 uses SZP  and script2 uses DZP.
       

15
General Questions and Answers / The question of screeing layers including electrode copies
« on: May 16, 2017, 03:32 »
Dear Quantumwise staffs
         We know from ATK ver.10.8 , the screening layers include electrode copies : http://quantumwise.com/documents/tutorials/latest/UpgradeGuide/index.html/chap.upgrade.html#sect1.upgrade.twoprobe. Functions of electrode copies is extend screening areas to make electrostatic difference potential smoothly apporach potentials of electrodes, right? But what about electrostatic difference potential always drop along the whole central region such as Fig.1? In Fig.1, electrostatic difference potential is calculated by 0V.nc and 0.5V.nc. Can we use datas from 0.5V.nc to get correct results?
         Best

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