gollum5s

 

GOLLUM is a program written Matlab that computes the electrical and thermal transport properties of multi-terminal nano-scale systems. The program can compute transport properties of either user-defined systems described by a tight-binding (or Huckel) Hamiltonian, or more material-specific properties of systems composed of real atoms described by DFT Hamiltonians. The program has been designed to interface easily with any DFT code, which uses a localized basis set and currently reads information from SIESTA. Plans to generate interfaces to other codes like FIREBALL are underway.

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GOLLUM is based on equilibrium transport theory, which means that it consumes much less memory than NEGF codes. The program has been designed for user-friendliness and takes a considerable leap towards the realization of ab initio multi-scale simulations of conventional and more sophisticated transport functionalities. These include:

Simulates multi-terminal devices
Gollum simulates the transport properties of a junction connected to an arbitrary number of leads. These leads can be narrow or wide.


Reads either Tight-Binding or DFT Hamiltonians
Gollum assumes that the Hamiltonians describing the junction expanded in terms of a localized basis set. Gollum reads this Hamiltonians from files. For tight-binding models, these files can easily be written by hand (for very simple systems), or using a tight-binding Hamiltonian if the junction is too big. They can also be generated by any localized basis set-based DFT code. Notice that for wide enough leads displaying a high crystalline structure, a mixed localized basis set that includes transverse k-points might be needed. Gollum can simulate easily these junctions.


Computes the full scattering matrix
Gollum computes the full scattering matrix of the junction for all open incoming and outgoing channels, including their modules and phases. Because the information is too long, it prints only those channels placed at the Fermi energy (Mode-2 of Gollum).


Computes charge transport
Gollum computes the spin-dependent transmission and shot-noise coefficients among any two given leads of a junction in equilibrium conditions, as well as the number of open channels and reflection coefficient of each lead (Mode-1 of Gollum). 


Computes heat transport
Gollum computes the electrical and thermal conductance, as well as the Peltier and Seebeck coefficients between any two leads of the junctions, as a function of Temperature (Mode-3 of Gollum). 


Computes spin transport
Gollum can treat paramagnetic junctions, as well as those displaying spin-polarized collinear magnetic properties. More generally, Gollum can also handle junctions possessing any non-trivial non-collinear spin arrangement. Furthermore, it can also compute the transport properties of junctions displaying strong spin-orbit effects, like those made of Topological Insulator materials, or where the scattering region has strong magnetic anisotropies (Mode-1, 2 and 4 of Gollum).


Computes I-V curves
Gollum computes the spin-dependent transmission coefficients of a junction whose leads are subjected to arbitrary voltages. It can automatically ramp up the voltage of one of the leads to generate I-V curves (Mode-4 of Gollum).


Handles vdW and LDA+U functionals
The flexible file format used in Gollum has enabled us to create interfaces to all the latest flavours of the SIESTA code, including those featuring the vdW and LDA+U functionals.

 

Scissors corrections scheme for strongly correlated systems

DFT-based estimates of the electronic structure of nanometer-sized quantum systems tend to under-estimate their HOMO-LUMO gap (e.g.: the energy separation between the highest occupied and the lowest unoccupied eigen-states of the quantum system). If the quantum system is connected to external leads to make a junction, the above fault translates into a gross overestimation of the conductance of the junction. The scissors correction scheme is a phenomenological correction to the DFT Hamiltonian that places the quantum levels at roughly their correct energy position, rendering transport results that compare satisfactorily with experiments. Furthermore, the scheme is enhanced to include screening effects on the quantum system due to the presence of nearby metallic surfaces – the electrodes.


Computes band-structure of the leads and density of states (DOS) in the scattering region

Gollum computes the band structure of the crystalline leads. These bands structures are plotted having k in the y-axis and E in the x-axis, as GOLLUM fixes E and then find those wave-vectors satisfying the Schrodinger equation. Gollum also picks the Hamiltonian of the scattering region, isolates it from the electrodes and computes its DOS with and without scissors corrections.


Covers large samples enabling to analize ballistic to diffusive regime

Gollum can compute the transport properties of very large samples for any given Hamiltonian (tight-binding or DFT). This fact enables us to go over from the ballistic to the diffusive regimes.

 

Version info:

The current GOLLUM "version" is: 1.1.1 released on May 2015.

The first version of GOLLUM v.1.0 was released on 10 July 2014.

GOLLUM is updated continuously. Whenever we fix a bug or add a feature, we release it immediately, and post a notice on the website and email to GOLLUM mailing list.

If you have a problem that you are convinced is a GOLLUM code issue or have suggestions for further development, please send an email to Dr. Hatef Sadeghi (This email address is being protected from spambots. You need JavaScript enabled to view it.).

 
Version 2.0 will come with

  •     **  Kondo & Coulomb blockade physics
  •     **  Magnetic field and quantum Hall
  •     **  Improved algorithms for larger samples.
  •     **  Info about Local charge, spin, current and spin-current densitie
  •     **  Interface to plane-wave codes using Wannier90 code


GOLLUM Licence Holders:

jaimes

Prof. Jaime Ferrer

Universidad de Oviedo

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            colinls

Prof. Colin J. Lambert

Lancaster University

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victorss

Dr. Víctor García-Suárez

Universidad de Oviedo

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  hss

Dr. Hatef Sadeghi

Lancaster University

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steves

Dr. Steve Bailey

Lancaster University

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GOLLUM currently-active “Authors”:

jaimes

Prof. Jaime Ferrer

Universidad de Oviedo

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            hss

Dr. Hatef Sadeghi

Lancaster University

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victorss

Dr. Víctor García-Suárez

Universidad de Oviedo

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  davids

Dr. David Visontai

Lancaster University  

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steves

Dr. Steve Bailey

Lancaster University

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Dr. Sara Sangtarash

Lancaster University

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GOLLUM past “Authors”:

lazlos

Dr. Laszlo Oroszlany

Budapest University of

Technology and Economics

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Dr. David Zs. Manrique

Lancaster University

          

 
robins

Rubén Rodríguez-Ferradás

Universidad de Oviedo

          katas

Dr. Katalin Gillemot

Lancaster University

laiths

Dr. Laith Algharagholy

Al-Qadisiyah University

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Dr. Iain Grace

Lancaster University

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Zain Y. Mijbil

Lancaster University

     

 

Sailing to Piel Island

 

 

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