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conductance_calculation_using_green_s_function_method

This page describes how to calculate transport properties using Fireball. First, we need to obtain SCF-solution for particular geometry. Once we have it, we need to switch on these options:

```ifixcharge = 1
itrans = 1```

Simulation parameters are defined in two additional files:

`trans.optional` This file defines basic parameters of the transport calculation.

```1                    ! ieta (use extra imaginary part of selected part )
1                    ! iwrt_trans (dump extra information)
0                    ! ichannel (perform eigenchannel analysis)
0                    ! ifithop (fitting hoppings at larger distances)
0.0                 ! bottom energy level
1.0                 ! top energy level
5                   ! number of the energy steps
0.05                 ! imaginary part```

`interaction.optional` In used formalism the system is divided into two subsystems (1,2). The transport calculation is calculated in interface between these two. The division of the system into two is defined in file `'interaction.optional`' with following format:

```0                      ! number of neighbors cell involved in the calculation of sample1
112                    ! total number of atoms in the sample1
1                      ! number of intervals defining the sample1
1    112               ! atom1 atom2 of the interval
4                      ! number of atoms in tip1
49,50,51,52            ! list of atoms in the tip1
0                      ! number of neighbors cell involved in the calculation of sample1
120                    ! total number of atoms in the sample2
1                      ! number of intervals defining the sample2
113  232               ! atom1 atom2 of the interval
7                      ! number of atoms in tip2
113,114,115,116,117,118,119          ! list of atoms in the tip2```

`eta.optional` Sometimes is convenient define a region where different imaginary part will be applied. In this case option `'ieta`' in `'trans.optional`' file has to be switched on. In addition, `'eta.optional`' file has to be presented, where atoms belonging to the region are listed. The file has following syntax:

```0.001               ! value of imaginary part
1                   ! number of intervals
65      168         ! first & last atoms in the interval```