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14: Linear Sodium Chain — Transport properties

  • Outline: Compare the quantum conductance of a periodic linear chain of Sodium atoms with that of a defected chain

  • Directories:

    • tutorials/tutorial14/periodic
    • tutorials/tutorial14/defected

    Files can be downloaded from here

  • Input Files

    • Na_chain.scf The pwscf input file for ground state calculation

    • Na_chain.nscf The pwscf input file to obtain Bloch states for the conduction states

    • Na_chain.pw2wan Input file for pw2wannier90

    • Na_chain.win The wannier90 input file

The periodic system contains two unit cells evenly distributed along the supercell. Transport calculations are performed using transport_mode = bulk and so the resulting quantum conductance represents that of an infinite periodic chain.

The part of the wannier90 input file that controls the transport part of the calculation looks like:

Input file
transport = true
transport_mode = bulk
tran_read_ht = false
one_dim_axis = x
fermi_energy = -2.7401
tran_win_min = -5.0
tran_win_max = 5.0
tran_energy_step = 0.01
translation_centre_frac = 0.5 0.5 0.5
tran_num_bb = 2

The defected system uses a 13 atom supercell with the central atom position altered to break symmetry. Setting transport_mode = lcr with tell wannier90 to treat the system as an infinite system with the defect at its centre. The supercell is chosen so that is conforms to the 2c2 geometry (see User Guide for details). Each principal layer is 2 atoms long so that the conductor region contains the defected atom plus a single atom on either side.

The transport section of the input file contains these key differences:

Input file
transport_mode = lcr
tran_num_ll = 2
tran_num_cell_ll = 2

Descriptions of these and other keywords related to the calculation of transport properties can be found in the User Guide.

  1. Run pwscf and wannier90 for the periodic system.

  2. Run pwscf and wannier90 for the defected system.

  3. The quantum conductance is written to the files periodic/Na_chain_qc.dat and , respectively. Compare the quantum conductance of the periodic (bulk) calculation with the defected (LCR) calculation. Your plot should look like this.

Image title
Quantum conductance of periodic Sodium chain (black) compared to that of the defected Sodium chain (red).