why are there so many electrons in the scatter region?

[Old Horse]

Dear all
       I perform a calculation of the transport property of a (4,4) carbon nanotube. I use two (4,4) carbon nanotubetwo as electrodes . The three part of the two probe system form a perfect nanatube. There are 96 C atoms in the scattering region, and there should be 384 valent electrons. However, after the SCF calculation, I found that the electron numbers are 418 and 431 respectively for a constraints and unconstraints calculation (ElectrodeConstraints.Off or ElectrodeConstraints.RealSpaceDensity). Why are there so many electron? is the current I obtained valid then?

[Anders Blom]

Please post the complete output file, it makes it easier to see exactly where the electrons are (if you used verbosity 10), or at least if there is a substantial difference in the equivalent bulk run compared to the two-probe part.

[Old Horse]

I use verbosity_level = 1, following are the out put, a new run with  verbosity_level = 10 is just doing and will be post as it finished
# ----------------------------------------------------------------
# Electrodes Calculation
# ----------------------------------------------------------------
# sc  0 : Fermi Energy =    0.00000 Ry
# sc  1 : Fermi Energy =   -0.38482 Ry  Ebs =  -69.59765 Ry  dRho = 1.8559E+000  dEbs = -6.9598E+001 Ry  dH = 3.7595E-001 Ry
# sc  2 : Fermi Energy =   -0.36778 Ry  Ebs =  -68.21261 Ry  dRho = 2.8235E-002  dEbs = 1.3850E+000 Ry  dH = 2.7573E-001 Ry
# sc  3 : Fermi Energy =   -0.31569 Ry  Ebs =  -63.98580 Ry  dRho = 7.5905E-002  dEbs = 4.2268E+000 Ry  dH = 1.0057E-001 Ry
# sc  4 : Fermi Energy =   -0.29778 Ry  Ebs =  -62.50458 Ry  dRho = 3.6564E-002  dEbs = 1.4812E+000 Ry  dH = 2.1447E-002 Ry
# sc  5 : Fermi Energy =   -0.29213 Ry  Ebs =  -61.93379 Ry  dRho = 1.6746E-002  dEbs = 5.7079E-001 Ry  dH = 1.2636E-002 Ry
# sc  6 : Fermi Energy =   -0.29302 Ry  Ebs =  -62.00071 Ry  dRho = 1.4925E-003  dEbs = -6.6916E-002 Ry  dH = 8.7399E-003 Ry
# sc  7 : Fermi Energy =   -0.29485 Ry  Ebs =  -62.09522 Ry  dRho = 1.6612E-003  dEbs = -9.4507E-002 Ry  dH = 1.8684E-003 Ry
# sc  8 : Fermi Energy =   -0.29693 Ry  Ebs =  -62.20649 Ry  dRho = 7.7246E-004  dEbs = -1.1127E-001 Ry  dH = 2.9996E-003 Ry
# sc  9 : Fermi Energy =   -0.29643 Ry  Ebs =  -62.16736 Ry  dRho = 1.0073E-003  dEbs = 3.9127E-002 Ry  dH = 5.8922E-004 Ry
# sc 10 : Fermi Energy =   -0.29674 Ry  Ebs =  -62.18297 Ry  dRho = 1.6458E-004  dEbs = -1.5613E-002 Ry  dH = 1.1748E-004 Ry
# sc 11 : Fermi Energy =   -0.29675 Ry  Ebs =  -62.18302 Ry  dRho = 1.3439E-005  dEbs = -4.5469E-005 Ry  dH = 8.7170E-005 Ry
# sc  0 : Fermi Energy =    0.00000 Ry
# sc  1 : Fermi Energy =   -0.38086 Ry  Ebs =  -68.78517 Ry  dRho = 1.8392E+000  dEbs = -6.8785E+001 Ry  dH = 2.4571E-001 Ry
# sc  2 : Fermi Energy =   -0.36384 Ry  Ebs =  -67.44524 Ry  dRho = 1.4385E-002  dEbs = 1.3399E+000 Ry  dH = 1.9794E-001 Ry
# sc  3 : Fermi Energy =   -0.29667 Ry  Ebs =  -62.11998 Ry  dRho = 6.3980E-002  dEbs = 5.3253E+000 Ry  dH = 1.7639E-002 Ry
# sc  4 : Fermi Energy =   -0.29652 Ry  Ebs =  -61.90026 Ry  dRho = 1.7505E-002  dEbs = 2.1972E-001 Ry  dH = 1.6893E-002 Ry
# sc  5 : Fermi Energy =   -0.28661 Ry  Ebs =  -61.09031 Ry  dRho = 1.1313E-002  dEbs = 8.0996E-001 Ry  dH = 1.6676E-002 Ry
# sc  6 : Fermi Energy =   -0.28950 Ry  Ebs =  -61.30338 Ry  dRho = 2.3269E-003  dEbs = -2.1307E-001 Ry  dH = 9.8091E-003 Ry
# sc  7 : Fermi Energy =   -0.29288 Ry  Ebs =  -61.52208 Ry  dRho = 1.6173E-003  dEbs = -2.1871E-001 Ry  dH = 3.7776E-003 Ry
# sc  8 : Fermi Energy =   -0.29457 Ry  Ebs =  -61.61971 Ry  dRho = 5.3327E-004  dEbs = -9.7630E-002 Ry  dH = 1.5319E-003 Ry
# sc  9 : Fermi Energy =   -0.29444 Ry  Ebs =  -61.60775 Ry  dRho = 2.8972E-004  dEbs = 1.1967E-002 Ry  dH = 1.6840E-003 Ry
# sc 10 : Fermi Energy =   -0.29514 Ry  Ebs =  -61.65888 Ry  dRho = 5.8815E-004  dEbs = -5.1135E-002 Ry  dH = 3.7422E-005 Ry
# sc 11 : Fermi Energy =   -0.29515 Ry  Ebs =  -61.65905 Ry  dRho = 9.1541E-006  dEbs = -1.6688E-004 Ry  dH = 3.0127E-005 Ry
# ----------------------------------------------------------------
# Equivalent Bulk Calculation (Initial Density for TwoProbe)
# ----------------------------------------------------------------
# sc  0 : Fermi Energy =    0.00000 Ry
# sc  1 : Fermi Energy =   -0.38074 Ry  Ebs = -552.56692 Ry  dRho = 1.8729E+000  dEbs = -5.5257E+002 Ry  dH = 3.6268E-001 Ry
# sc  2 : Fermi Energy =   -0.37559 Ry  Ebs = -549.31003 Ry  dRho = 7.0420E-003  dEbs = 3.2569E+000 Ry  dH = 3.3537E-001 Ry
# sc  3 : Fermi Energy =   -0.29756 Ry  Ebs = -499.99741 Ry  dRho = 1.1402E-001  dEbs = 4.9313E+001 Ry  dH = 8.5807E-002 Ry
# sc  4 : Fermi Energy =   -0.30158 Ry  Ebs = -501.94452 Ry  dRho = 1.7386E-002  dEbs = -1.9471E+000 Ry  dH = 4.6462E-002 Ry
# sc  5 : Fermi Energy =   -0.27933 Ry  Ebs = -487.57936 Ry  dRho = 3.2493E-002  dEbs = 1.4365E+001 Ry  dH = 6.5018E-002 Ry
# sc  6 : Fermi Energy =   -0.28388 Ry  Ebs = -489.84275 Ry  dRho = 1.0773E-002  dEbs = -2.2634E+000 Ry  dH = 2.8395E-002 Ry
# sc  7 : Fermi Energy =   -0.28664 Ry  Ebs = -491.15145 Ry  dRho = 2.6061E-003  dEbs = -1.3087E+000 Ry  dH = 1.2352E-002 Ry
# sc  8 : Fermi Energy =   -0.28778 Ry  Ebs = -491.84633 Ry  dRho = 1.3781E-003  dEbs = -6.9488E-001 Ry  dH = 1.0109E-002 Ry
# sc  9 : Fermi Energy =   -0.29124 Ry  Ebs = -493.73057 Ry  dRho = 2.3066E-003  dEbs = -1.8842E+000 Ry  dH = 2.8443E-003 Ry
# sc 10 : Fermi Energy =   -0.29230 Ry  Ebs = -494.31810 Ry  dRho = 8.9495E-004  dEbs = -5.8753E-001 Ry  dH = 1.7153E-003 Ry
# sc 11 : Fermi Energy =   -0.29278 Ry  Ebs = -494.41671 Ry  dRho = 8.0515E-004  dEbs = -9.8605E-002 Ry  dH = 1.0004E-003 Ry
# sc 12 : Fermi Energy =   -0.29289 Ry  Ebs = -494.45677 Ry  dRho = 9.6865E-005  dEbs = -4.0060E-002 Ry  dH = 9.4689E-004 Ry
# sc 13 : Fermi Energy =   -0.29329 Ry  Ebs = -494.60205 Ry  dRho = 2.1890E-004  dEbs = -1.4528E-001 Ry  dH = 4.1363E-004 Ry
# sc 14 : Fermi Energy =   -0.29329 Ry  Ebs = -494.59644 Ry  dRho = 7.2030E-005  dEbs = 5.6127E-003 Ry  dH = 1.6898E-004 Ry
# sc 15 : Fermi Energy =   -0.29330 Ry  Ebs = -494.59801 Ry  dRho = 2.7905E-005  dEbs = -1.5687E-003 Ry  dH = 1.4534E-004 Ry
# ----------------------------------------------------------------
# TwoProbe Calculation
# ----------------------------------------------------------------
# sc  0 : q =  383.99017 e
# sc  1 : q =  412.97473 e  Ebs = -354.49262 Ry  dRho = 1.3014E+002  dEbs = -3.5449E+002 Ry  dH = 5.6512E-001 Ry
# sc  2 : q =  414.47407 e  Ebs = -360.82747 Ry  dRho = 4.1782E+000  dEbs = -6.3349E+000 Ry  dH = 3.6826E-001 Ry
# sc  3 : q =  416.83350 e  Ebs = -370.41142 Ry  dRho = 5.0302E+000  dEbs = -9.5839E+000 Ry  dH = 1.3006E-001 Ry
# sc  4 : q =  417.42461 e  Ebs = -371.43589 Ry  dRho = 2.6024E+000  dEbs = -1.0245E+000 Ry  dH = 7.9374E-002 Ry
# sc  5 : q =  418.13382 e  Ebs = -373.14609 Ry  dRho = 2.3687E+000  dEbs = -1.7102E+000 Ry  dH = 6.2686E-002 Ry
# sc  6 : q =  417.93744 e  Ebs = -372.48404 Ry  dRho = 7.5953E-001  dEbs = 6.6205E-001 Ry  dH = 5.4537E-002 Ry
# sc  7 : q =  418.99944 e  Ebs = -376.07679 Ry  dRho = 2.8583E+000  dEbs = -3.5928E+000 Ry  dH = 9.5793E-002 Ry
# sc  8 : q =  418.10739 e  Ebs = -372.70887 Ry  dRho = 1.8139E+000  dEbs = 3.3679E+000 Ry  dH = 5.3472E-002 Ry
# sc  9 : q =  418.49108 e  Ebs = -374.21267 Ry  dRho = 9.1968E-001  dEbs = -1.5038E+000 Ry  dH = 9.8387E-003 Ry
# sc 10 : q =  418.44168 e  Ebs = -374.00448 Ry  dRho = 9.6490E-002  dEbs = 2.0819E-001 Ry  dH = 4.2329E-003 Ry
# sc 11 : q =  418.46548 e  Ebs = -374.14441 Ry  dRho = 1.0174E-001  dEbs = -1.3993E-001 Ry  dH = 2.2833E-003 Ry
# sc 12 : q =  418.45230 e  Ebs = -374.10146 Ry  dRho = 2.5784E-002  dEbs = 4.2953E-002 Ry  dH = 6.8800E-004 Ry
# sc 13 : q =  418.45086 e  Ebs = -374.10787 Ry  dRho = 7.3693E-003  dEbs = -6.4170E-003 Ry  dH = 5.3064E-004 Ry
# sc 14 : q =  418.45132 e  Ebs = -374.11474 Ry  dRho = 5.7638E-003  dEbs = -6.8673E-003 Ry  dH = 4.6244E-004 Ry
# sc 15 : q =  418.45306 e  Ebs = -374.13005 Ry  dRho = 1.7255E-002  dEbs = -1.5309E-002 Ry  dH = 2.9308E-004 Ry
# sc 16 : q =  418.45328 e  Ebs = -374.13256 Ry  dRho = 2.2903E-003  dEbs = -2.5129E-003 Ry  dH = 2.6709E-004 Ry

[Anders Blom]

Although I haven't seen the geometry, my guess is that the electrode is too short. If it's only 1 period, or even 2, this is too short and will, even if the calculation converges (which is sometimes hard, when the electrodes are too short), lead to the wrong results.

It was observant of you to note the charges, but you would probably have seen it very clearly in the transmission spectrum later. This is an ideal system, but I would not be surprised if the transmission spectrum comes out less than perfect (not integer plateaus).

So, increase the electrodes (use 4 periods) and let's see what happens!

[Old Horse]

yes, just as you say, I use only one period. Now I reset it to 4 period and and see what happen!
thanks