## Attachment 'transport_1dmodel.py'

```   1 import Numeric
2 from ASE.Transport import TransmissionTools
3 from ASE.Transport.ScatteringHamiltonianMatrix import ScatteringHamiltonianMatrix
5
6 # Construct a lead Hamiltonian matrix describing 2 principal layers of
7 # a 1d TB chain with up to second-nearest neighbor hopping
8
10
11 # On-site energies are zero
12 for i in range(4):
14 # Nearest neighbor hopping is -1.0
15 for i in range(3):
18 # Next-nearest neighbor hopping is 0.2
19 for i in range(2):
22
23 # Construct the Hamiltonian of the scattering region including 1 principal
24 # layer of the lead. The scattering region consists of 2 sites at zero
25 # energy and with external coupling of 0.2 and internal coupling og 0.8.
26
27 H_scat=Numeric.zeros([6,6],Numeric.Complex)
28
29 # Principal layers
32 # Scattering region
33 H_scat[2,2]=0.0
34 H_scat[3,3]=0.0
35 H_scat[2,3]=0.8
36 H_scat[3,2]=0.8
37 # External coupling
38 H_scat[1,2]=0.2
39 H_scat[2,1]=0.2
40 H_scat[3,4]=0.2
41 H_scat[4,3]=0.2
42
43
44 # Initializing classes to contain scattering and lead Hamiltonians
45 # Principal layer is two sites and is the same for left and right leads
46 prin=2
47 hmat=ScatteringHamiltonianMatrix(leftprincipallayer=prin,rightprincipallayer=prin,hamiltonianmatrix=H_scat)
50
51 # Calculate transmission function at energies
52 en=Numeric.arange(-3,3,0.02)
53
54 #####################################################################################
55 # The following illustrates how to manipulate the Hamiltonian for analysis          #
56 # purposes. In particular it is shown how to (i) sub-diagonalize a subspace to      #
57 # obtain renormalized energy levels in a certain region. (ii) How to cut the        #
58 # coupling to selected orbitals e.g. some of the renormalized energy levels.        #
59 #####################################################################################
60
61 # Sub-diagonalize the subspace of the two sites to obtain two (renormalized) energy levels
62 from ASE.Utilities.Wannier import HamiltonianTools
63 H=hmat.GetHamiltonianMatrix()
64 # H has dimension 6x6 corresponding to the scattering region (two levels).
65 # The two levels thus have indices 2 and 3
66 states=[2,3]
67 # Sub-diagonalize the subspace of the two sites to obtain two (renormalized) energy levels
68 H2,U,eig=HamiltonianTools.SubDiagonalize(H,states)
69 print "The renormalized molecular energy levels",eig
70 # Cut all couplings to one of the two levels. This level is now effectively removed
71 # from the calculation, and only the other level will show up as a peak in the transmission.
72 H3=HamiltonianTools.CutCoupling(H2,[3])
73 hmat.SetHamiltonianMatrix(H3)
74
75 # Initialize Transmission object
76 trans=TransmissionTools.TransmissionTool(hmat,left,right,en,prin)
77 trans.InitGreenFunctions()
78
79 # We want to calculate:
80 # the transmission function and the spectral functions of all sites in scattering region
81 trans.UpdateTransmission()
83
84 # Run calculation
85 t=trans.UpdateToNetCDFFile('TBchain_trans.nc')
```

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• [get | view] (2006-02-09 10:38:07, 3.3 KB) [[attachment:transport_1dmodel.py]]
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