At first, openmx
calculates the transmission, the total current,
and the conductance.
The relevant keywords for the calculation are as follows:
NEGF.tran.Analysis on # default on NEGF.tran.CurrentDensity on # default on NEGF.tran.energyrange 10 10 1.0e3 # default=10.0 10.0 1.0e3 (eV) NEGF.tran.energydiv 200 # default=200 NEGF.tran.Kgrid 1 1 # default= 1 1
NEGF.tran.Analysis
, NEGF.tran.Channel
,
NEGF.tran.CurrentDensity
If NEGF.tran.Analysis
is set to on
,
the transmission, the total current, and the conductance are calculated.
NEGF.tran.energyrange
,
NEGF.tran.energydiv
The energy range where the transmission is calculated is given by the keyword 'NEGF.tran.energyrange', where the first and second numbers correspond to the lower and upper bounds, and the third number is an imaginary number used for smearing out the transmission. The energy range specified by 'NEGF.tran.energyrange' is divided by the number specified by the keyword 'NEGF.tran.energydiv'.
NEGF.tran.Kgrid
The numbers of kpoints to discretize the reciprocal vectors and are specified by the keyword 'NEGF.tran.Kgrid'. The set of numbers given by 'NEGF.tran.Kgrid' can be different and tends to be larger than that by 'NEGF.scf.Kgrid' to take account of the computational efficiency.
In the calculations of the transmission, the current, and the conductance, following messages are printed in the standard output.
******************************************************* ******************************************************* Welcome to TRAN_Main_Analysis. This is a postprocessing code of OpenMX to analyze transport properties such as electronic transmission, current, eigen channel, and current distribution in real space based on NEGF. Copyright (C), 20022015, H. Kino and T. Ozaki TRAN_Main_Analysis comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to redistribute it under the constitution of the GNUGPL. ******************************************************* ******************************************************* Chemical potentials used in the SCF calculation Left lead: 5.125617225230 (eV) Right lead: 5.125617225230 (eV) NEGF.current.energy.step 1.0000e02 seems to be large for the calculation of current ... The recommended Tran.current.energy.step is 0.0000e+00 (eV). TRAN_Channel_kpoint 0 0.000000 0.000000 TRAN_Channel_energy 0 0.000000 eV TRAN_Channel_Num 5 Parameters for the calculation of the current lower bound: 5.125617225230 (eV) upper bound: 5.125617225230 (eV) energy step: 0.010000000000 (eV) imaginary energy 0.001000000000 (eV) number of steps: 0 calculating... myid0= 0 i2= 0 i3= 0 k2= 0.0000 k3= 0.0000 myid0= 1 i2= 0 i3= 0 k2= 0.0000 k3= 0.0000 Transmission: files ./negfchain.tran0_0 Current: file ./negfchain.current Conductance: file ./negfchain.conductance
After the calculations, in this case you will obtain three files
negfchain.tran0_0
,
negfchain.current
,
negfchain.conductance
:
The file stores transmissions for up and downspin states. The fourth column is the energy relative to the chemical potential of the left lead, and the sixth and eighth columns are transmission for up and downspin states, respectively. When you employ a lot of kpoints which is given by 'NEGF.tran.Kgrid', a file with a different set of '#' and '%' in the file extension is generated for each kpoint. The correspondence between the numbers and the kpoints can be found in the file.
The file stores kresolved currents and its average for up and downspin states in units of ampere.
The file stores kresolved conductance and its average for up and
downspin states in units of quantum conductance (
).
Thus, the conductance is proportional to the transmission
at the chemical potential of the left lead, , as follows:
As an example, the kresolved transmission drawn by
using the file 'System.Name.conductance' is shown in Fig. 41.
