Dear Mengqiu: I think the answer is simple, but I will explain in a bit long detail:
The parameters: TS.TBT.Emin TS.TBT.Emax Define the minimum and maximum energy values considered to compute the function "Transmission(E)" (We are talking about the total energy of the electrons incident to the scattering region). These two values are used together with TS.TBT.NPoints to tell the program how this function "Transmission(E)" is going to be sampled (numerically) i.e. the program tbtrans will produce a table with values of energy (E) and Transmission (T): E1 T1 E2 T2 E3 T3 ... ... ... En Tn - Such that "E1 < E2 < E3 < E4 ... < En" and they are equi-spaced (regular spacing sampling in Energy) - Such that E1 = TS.TBT.Emin - Such that En = TS.TBT.Emax - And such that n = TS.TBT.NPoints So these labels define the interval and sampling chosen for the computation of "Transmission(E)", ( T(E)). For a given bias voltage (V). The electron current, I, is computed using that function T(E). I is basically the definite integral of T(E) to a given window of energies. That window of energies (for the integral) is just proportional to the the bias voltage V (the integral runs from -eV/2 to eV/2). So if you have chosen a sampling for T(E) such that the interval of energies sampled does not include the bias voltage "window", then the program runs into trouble since it can not compute the integral for I properly. Therefore, the suggestion is clear: - Make E1 and En such that the interval (-eV/2, eV/2) is included in the interval (E1,En). - Also choose a large enough number of points to describe the function T(E) properly! (it may have sharp peaks) Other than that, TS.TBT.Emin, TS.TBT.Emax and TS.Voltage are independent parameters. This means that, for a given bias voltage and as longas the interval (TS.TBT.Emin, TS.TBT.Emax) is large enough (in the sense explained above), the current computed should not change if you vary TS.TBT.Emin, TS.TBT.Emax. Yours Jose A. Torres, Ph.D. SIESTA Manager On Tue, 2010-06-15 at 19:06 +0200, Marcos Veríssimo Alves wrote: > Sorry Cai, never performed a transport calculation in my life... Maybe > someone else in the list can help you. > > > Good luck, > > > Marcos > > 2010/6/15 CaiMeng-Qiu <caimeng...@hotmail.com> > > Dear Marcos: > I want to get the I-V curve. But I do not know how to > decide the range of the parameter of TS.TBT.Emax and > TS.TBT.Emin by the value of TS.voltage. As the manual of > Siesta-3.0-b says, the TS.TBT.Emax and TS.TBT.Emin mean > the highest and lowest value of the computed transmission > function. It is also noted that the current will be computed > using the resulting transmission function, so be sure to make > it suited for the integration in the bias window (the energy > window defined by TS.TBT.Emin and TS.TBT.Emax being bigger > than or equal to the applied bias). > > Based the upon principle, I think that we will obtain the > special value of current for the given voltage as long as the > bias window between the energy window defined by TS.TBT.Emin > and TS.TBT.Emax . > > For example, I think that, supposed the selected valtage 1.0 > eV, the b ias window is -0.5eV-0.5 eV. So the value of > TS.TBT.Emin should be less than -0.5 eV and the value of > TS.TBT.Emax should be larger than 0.5 eV. Is it right? Please > tell me how to decide the range of the parameter of > TS.TBT.Emax and TS.TBT.Emin based on the TS.voltage? > > For the second question, I do not know why, for the given > voltage (such as 1.0 eV), the value of current is changed for > the different energy window defined by TS.TBT.Emin and > TS.TBT.Emax.? I think that we will obtain the special value of > current for the given voltage as long as the bias window > between the energy window defined by TS.TBT.Emin and > TS.TBT.Emax . > For my system, the parameters are followed: > TS.Voltage 1.0 eV > TS.TBT.Emin -0.5 eV > TS.TBT.Emax 0.5eV > > I get the value of current is 4.17777609E-16 > > another thing: > > T S.Voltage 1.0 eV > TS.TBT.Emin -1.0 eV > TS.TBT.Emax 01.0 eV > > I get the value of current is 4.216753E-16 > > > Thank you very much in advance! > > Sincerely, > > Mengqiu > ------------------------------------------------------------- > M. Q. Cai, Ph.D, Prof. > School of Physics and Microelectronics Science, > HunanUniversity, > Changsha410082, Hunan, > P. R. China > Tel: +86-731-8882-1177; 13107118489 > e-mail: caimeng...@hotmail.com > > > > > > ______________________________________________________________ > 使用新一代 Windows Live Messenger 轻松交流和共享！ 立刻下载！ > >
