Thank you Alexander! -Manoj On Fri, 3 Apr 2009, Alexander Smogunov wrote:
> Dear Manoj > > On Wednesday 01 April 2009 22:57, Manoj Srivastava wrote: > > Dear PWSCF users and developers, > > I have been trying to understand the PWCOND code for transmission > > calculation, basically 'transmit.f90' file. The wavefunction in the left > > lead, right lead and scattering region is given by - > > > > psi_k+sum_{k'}r_{kk'}psi_k' > > psi= sum_{n} a_n psi_n+ sum_{\alpha l m} C_{\alpha l m}psi_{\alpha l m} > > sum_{k'}t_{kk'}psi_k' > > > > The above expression is from Choi & Ihm's paper, on which I believe PWCOND > > is based on. Now undetermined coefficients in above expression are > > r_{kk'}, a_n, C_{\alpha,l,m}, t_kk'. I am confused on code evaluates these > > coefficients. My understanding is you first get the wavefunction in the > > leads and then solve scattering region the same way to get the > > wavefunction in scattering region, so at this point you have already > > determined a_n and C_{\alpha,l,m}. At last do boundary matching condition > > between leads and scattering region to get reflection and transmission > > coefficient. Am I right? > No, the scattering state (SS) is completely determined by unknown > coefficients which are: {r_kk', a_n, a_alpha, t_kk'}, the first defines the > SS in the left lead, the two next in the scattering region, and the last one > in the right lead. What you have found before are just basis solutions phi_n > and phi_alpha of the Sroedinger eq. in the scattering region over which you > expand the SS with coefficients (unknown yet) a_n and a_alpha. > > Hope this helps, > Alexander > > > My thinking is based on simple quantum mechanics > > scattering problem where we solve schrodinger's equation in each region > > and then do boundary matching to get reflection and transmission > > coefficients. > > > > Now looking at the subroutine 'transmit.f90', this does not appear to be > > the case. It seems as if we are solving the Schrodinger's equation in the > > scattering region and doing boundary matching at the same time. Using a > > big matrix and solving something like AX=B. Would anybody mind explaing > > what's going on in subroutine transmit.f90? > > > > Regards, > > Manoj Srivastava > > Physics Graduate Student > > University Of Florida, Gainesville, FL > > > > _______________________________________________ > > Pw_forum mailing list > > Pw_forum at pwscf.org > > http://www.democritos.it/mailman/listinfo/pw_forum > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >