Messages

1

General Questions and Answers / Re: Extracting the hamiltonian for an unit cell of a Nanowire

« on: November 10, 2015, 14:39 »

To construct a nanowire in arbitrary directions, in the builder open builders->nanowire . It use the Wulff construction to setup the nanowire geometry. 

To get out the hamiltonian, see the tutorial:
http://quantumwise.com/documents/tutorials/latest/LowLevelEntities/index.html/

2

General Questions and Answers / Re: Integrating DOS

« on: October 20, 2015, 14:44 »

You may also use the Bader charge plugin in VNL to get the bader charges on each atom. This is the standard approach to get a charge on each atom.

3

General Questions and Answers / Re: temperature distribution along the device length

« on: October 12, 2015, 16:04 »

This is not possible. The only temperature you can specify, is the temperature in the electrode. This temperature defines the electronic temperature, i.e. the temperature of the Fermi distribution.

However, inside the device a temperature distribution would affect the phonon distibution. One method to include this is to make a MD simulation with different thermal couplings in different parts of the device and then perform transport calculations on the MD snapshots.

For using different thermal couplings see:
http://www.quantumwise.com/publications/tutorials/item/834-calculating-interfacial-thermal-conductance-using-molecular-dynamics

For the transport through the MD snapshot you can get inspired by:
http://www.quantumwise.com/publications/tutorials/item/832-elastic-scattering-mean-free-path-mobility-impurity-scattering-in-a-silicon-nanowire

4

General Questions and Answers / Re: Mobility / first-order DP

« on: October 9, 2015, 09:15 »

We include all modes, both optical and acustic, there is now a tutorial online
http://docs.quantumwise.com/tutorials/atk/mobility/mobility.html?highlight=mobility

5

General Questions and Answers / Re: Phase Transition in Materials

« on: September 28, 2015, 23:00 »

For the Classical potential you need to check if it was developed for your system,  else you will need to use DFT. You can use ATK-Classical to find an appropriate time-step and check other parameters of the MD simulation, I recommend the tutorial,
http://www.quantumwise.com/publications/tutorials/item/732-basic-molecular-dynamics-tutorial

With the DFT you should save the trajectory and then you can follow the simulation by inspecting the trajectory.
To see a 1. order phase transition, there must be a discontinuity in the potential energy as a function of temperature.  Thus,  you can forinstance slowly heat up the system, and if there is no phase transition both the temperature and potential energy will increase slowly, upon the phase transition temperature will be constant and the potential energy will change suddently.

6

General Questions and Answers / Re: Hamiltonian Calculation

« on: September 28, 2015, 22:46 »

In ATK-2014 there are build in functions for getting H and S, this is much simpler:
 see the tutorial
http://www.quantumwise.com/documents/tutorials/latest/LowLevelEntities/index.html/

7

General Questions and Answers / Re: e-ph coupling / IETS spectra...

« on: September 17, 2015, 13:45 »

please detail question 1, I do not understand it.

Regarding 2, there is a plugin to plot dI/dV vs V and d2I/d2V vs V. You can download the data and combine them to plot what you suggest.

8

General Questions and Answers / Re: EPC -constant/ Eliashberg function

« on: September 17, 2015, 13:42 »

There is a new plugin to visualize the epc, see attachment.

We have not implemented the Eliasberg function, we are working on making dH/DR available from LowLevelEntities, in this case it will be possible to implement it by yourself,

9

General Questions and Answers / Re: LOE approx.

« on: September 17, 2015, 13:27 »

1. The LOE approximation is only valid when the DOS is slowly energy dependent, you can always check by comparing with the XLOE approximation which includes the energy dependence.

2. Usually the e-ph coupling start to have an effect when the bias window is larger than the lowest energy phonon, thus, it is very system dependent what happens in the low bias regime,

10

General Questions and Answers / Re: Tr (k, e)/shift in Fermi level

« on: August 21, 2015, 11:29 »

The temperature enters the formalism through the fermi function, so it is an electron temperature.
Forinstance, at T=0 the conductance is given by the transmission coefficient at the fermi level, while for a finite temperature the transmission is averaged around the fermi level using the fermi function.

11

General Questions and Answers / Re: Fermi level pinning in thin layer oxide-semiconductor interface

« on: June 26, 2015, 14:20 »

Take a look at the tutorial:
http://www.quantumwise.com/publications/tutorials/item/820-ni-silicide-si-interfaces

We have applied same procedure to investigate interface traps in the AlGaAs-Al2O3 interface, see attachment

12

General Questions and Answers / Re: what cause the saltations? Is the results reliable?

« on: June 26, 2015, 14:11 »

Dear EdonChen,
Looks like a very interesting effect you have found. Interestingly there seems to be only some of the orbitals are affected. I would investigate the difference in the orbitals affected and those not.  I would also look at the voltage drop in the device before and after the jump, my guess is that the drop shifts position and maybe the charges in the molecule shifts positions.

I noted that the effect seems to be related with the HOMO entering the bias window. In this case the occupation of the Homo might drop and instead the occupation of the LUMO and LUMO+1 could increase.

Thus, I believe it is a correct effect of the calculation, hope my suggestions for investigating it helps.

13

Plugin Development / Re: Quantum espresso import/export plugin

« on: June 25, 2015, 14:08 »

There is improved support for Quantum Espresso in ATK-2015 to be released soon, and there is a short tutorial:

http://www.quantumwise.com/publications/tutorials/item/875-virtual-nanolab-as-gui-for-quantum-espresso

14

General Questions and Answers / Re: Checkpoint file in restarted calculations

« on: June 5, 2015, 21:55 »

# read configuration from checkpoint file
configuration = nlread('original_checkpoint_file.nc')[0]

# Define the check point handler
checkpoint_handler = CheckpointHandler('/home/checkpoint.nc', 20*Minute)

# Clone the calculator method, with a new checkpoint handler
calculator = configuration.calculator()(checkpoint_handler=checkpoint_handler)

configuration.setCalculator(calculator, initial_state=configuration)
configuration.update(force_restart=True)
nlsave('output.nc', configuration)

15

General Questions and Answers / Re: how to subtract contribution of different layer of layer material in T(E)

« on: April 15, 2015, 23:21 »

You can look at the transmission eigenstates and see how they decay through the device