Messages

1

General Questions and Answers / Re: what cause the saltations? Is the results reliable?

« on: June 27, 2015, 07:25 »

Thank you very much, professor Kstokbro, I am sincerely appreciate your help. And your  affirmation about the results makes me so excited.

Exactly, I've tried to find out the differences of the affected orbitals(LUMO&HOMO-2) and those not(HOMO&LUMO+2). But the MPSHs didnot show many remarkable differences, only HOMO-2 showed a difference of localized degree. And I also have tried to look into the differences of LDOS, PDOS, Effective Potential and electrostatic difference potential, Mulliken Population etc. before and after the jumps, but seems all fail to explain such phenomenon.
And I followed by your advice to calculate the voltage drop, as seen in attachment, since I am not quite familiar with voltage drop, Dear Kstokbro, do you think whether it might tell something?

"I noted that the effect seems to be related with the HOMO entering the bias window. In this case the occupation of the Homo might drop and instead the occupation of the LUMO and LUMO+1 could increase."
I don't quite understand this, because the HOMO has already entered into bias window before the jumps occur, in my GGA calculation, this jumps shift to ±1.55 V to ±1.60 V, while the HOMO still entered into bias window at ~±1.2V. So, I am anticipating your profound interpretation.

Thank you again for you kindly help!

2

General Questions and Answers / Re: what cause the saltations? Is the results reliable?

« on: June 26, 2015, 11:05 »

Could anyone do me a favor?
It's really a urgent trouble for me.
Thank you again!

3

General Questions and Answers / what cause the saltations? Is the results reliable?

« on: June 25, 2015, 11:39 »

Dear all,

There is a question that puzzled me for a long time.

My work is about a porphyrin-like molecule attachs to Au(111) electrodes, which forms a Metal-Molecule-Metal junction.

See the attachments, the molecular orbitals shift versus applied bias and I-V curve, the saltations occur in I-V curve and orbital shift at bias  from ±1.3 V to ±1.35 V, specifically, from 1.32V to 1.33V at positive voltage, and -1.34V to -1.35V at negative voltage. It was strange that not all the orbitals saltated at the above appiled biases.

In the beginning, we thought it was miscalculation or the effect of exchange-correlation potential, but our re-calculation, and change of exchange-correlation potential still showed the  characteristic.

So, what cause the saltations? Is the results reliable?

Any reply for me is helpful, thank you.

4

General Questions and Answers / About the alignments of HOMO&LUMO, and Mulliken Population

« on: May 4, 2015, 11:57 »

Dear all,

There are two questions that confused me about my recent work, and I need your help:

In my Metal-Molecule-Metal molecular junction(MMMs, or two-probe system), when calculates the EnergySpectrum of molecule in central region(ATK Version 2008), I've written down the atomic indices of atoms which formed the molecule, and uncheck the two CheckBoxs(Am I right to calculate the EnergySpectrum?) .

1)I first calculted the EnergySpectum naked molecule(in GGA.PBE exchange correlation potential),the QuantumNumbers of HOMO&LUMO are  254&255, respectively. However, when put into MMMs(weak coupling, in GGA.PBE exchange correlation potential), the two quantumNumber became 224&225, meanwhile, almost all the energy level of orbitals shift up ~4.7eV. So my question is whether the QuantumNumbers of HOMO&LUMO are 254&255 or 224&225 when calculates the MPSH of MMMs? What causes such upshift?

2)Through calculating the MullikenPopulation of central region, I found that the charges transferred from metal leads to the molecule under equilibrium circumstance, and the HOMO&LUMO asymmetrically aligned relates to FermiLevel of equivalent bulk markedly(LUMO closed to EF) at 0 bias. Is the alignment related to the charge transfer? In my several calculated systems, even the numerical values of transferred charge become smaller, the asymmetrical alignment had not significant change, why?

Thank you very much!
Sincerely.