Chimie Théorique » QMX

import numpy as np

import pylab

import ase.transport.stm as stm

#           Parameters for a simple model.

#

#

#                         * eps_a

#                 v_ts /   \ v_a2

#  ... *  *  *  *            *  *  *  *  * ...

#       \/                          \/

#       t1                          t2

#

#       Tip                      Surface

# ----------------|      |-----------------------

t1 = -1.0

t2 = -2.0

eps_a = 0.4

v_ts  = 0.05

v_a2 = 1.0

#Tip

h1 = np.zeros([2, 2])

h1[0, 1] = t1

h1[1, 0] = t1

s1 = np.identity(2)

h10 = np.zeros([2,2])

h10[0, 1] = t1

h10[1, 0] = t1

s10 = np.identity(2)

#Surface with "molecule" a.

h2 = np.zeros([2,2])

h2[0, 1] = v_a2

h2[1, 0] = v_a2

h1[0, 0] = eps_a

s2 = np.identity(2)

h20 = np.zeros([2,2])

h20[0, 1] = t2

h20[1, 0] = t2

s20 = np.identity(2)

#Tip Surface coupling

V_ts = np.zeros([2,2])

V_ts[1, 0] = v_ts

eta1 = 0.0001

eta2 = 0.0001

stm = reload(stm)

stm_calc = stm.STM(h1, s1, h2, s2, h10, s10, h20, s20, eta1, eta2)

energies = np.arange(-3.0, 3.0, 0.01)

stm_calc.initialize(energies)

T_stm = stm_calc.get_transmission(V_ts)

#Perform the full calculation and compare

from ase.transport.calculators import TransportCalculator as TC

h = np.zeros([4,4])

h[:2, :2] = h1

h[-2:, -2:] = h2

h[:2, -2:] = V_ts

h[-2:, :2] = V_ts.T

tc = TC(energies=energies,

        h=h,

        h1=h10,

        h2=h20,

        eta=eta1, eta1=eta1, eta2=eta2)

T_full = tc.get_transmission()

pylab.plot(stm_calc.energies, T_stm, 'b')

pylab.plot(tc.energies, T_full, 'r--')

pylab.show()

#bias stuff

biass = np.arange(-2.0, 2.0, 0.2)

Is = [stm_calc.get_current(bias, V_ts) for bias in biass]

pylab.plot(biass, Is, '+')

pylab.show()