Hi Anton,

Thanks for your two suggestions. I am able to perform the second method but I don't know how to call syst.modes. Would you please show me the codes using syst.modes to calculate DOS(energy=0) of my minimal example?
#-------------------------------------------------------------------
import kwant
import numpy 

a=1
W=30
t=1
lat = kwant.lattice.square(a)
syst = kwant.Builder(kwant.TranslationalSymmetry((-a, 0)))
syst[(lat(0, j) for j in range(W))] = 4 * t
syst[lat.neighbors()] = -t
fsyst = syst.finalized()

# Then how to use fsyst.modes to calculate DOS(energy=0) ?
#-------------------------------------------------------------------

Thanks in advance!

Regards,
Zhan

发件人：Anton Akhmerov <anton.akhmerov+kd@gmail.com>
发送日期：2019-12-21 21:55:34
收件人：Cao Zhan <caozhan@baqis.ac.cn>
抄送人：kwant-discuss <kwant-discuss@kwant-project.org>
主题：Re: [Kwant] Can Kwant calculate density of states of quasi one-dimensional systems?>Hi Zhan,
>
>SpectralDensity indeed doesn't support translationally invariant
>systems. You have two options instead. If you want to obtain the DOS
>at a specific energy, you should use the output of
>syst.modes—specifically the wave functions of the propagating modes.
>If you need the DOS of the full spectrum, you should diagonalize the
>Hamitlonian and perform a summation over all momenta on your own.
>
>Best,
>Anton
>
>On Sat, 21 Dec 2019 at 13:51, Cao Zhan <caozhan@baqis.ac.cn> wrote:
>>
>> Dear Kwant users,
>>
>> In Kwant manual there is a section entitled "Calculating spectral density with the kernel polynomial method". I find that examples in this section are all talking about finite-size systems. I wonder whether Kwant can calculate density of states of a quasi one-dimensional system that is finite along y-direction but is translationally invariant along x-direction. For a minimal test, I have run the following codes but errors occurred.
>> #--------------------------------------------------------------------------------------
>> import kwant
>> import numpy
>>
>> a=1
>> W=30
>> t=1
>> lat = kwant.lattice.square(a)
>> syst = kwant.Builder(kwant.TranslationalSymmetry((-a, 0)))
>> syst[(lat(0, j) for j in range(W))] = 4 * t
>> syst[lat.neighbors()] = -t
>> fsyst = syst.finalized()
>> energies = numpy.linspace(-0.1,0.1, 10)
>>
>> spectrum = kwant.kpm.SpectralDensity(fsyst)
>> spectrum.add_moments(10)
>> spectrum.add_vectors(5)
>> densities = spectrum(energies)
>> #--------------------------------------------------------------------------------------
>> What's wrong in above codes? Currently, are we able to employ Kwant to calculate density of states of 3D systems being translationally invariant along one or two directions?
>>
>> Regards,
>> Zhan
>>
>>
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