2016-11-12 19:53 GMT+01:00 Zara Nosh <[email protected]>: > Dear siesta users > > I have seen several transiesta examples in siesta package (Test and > Example directories); in all examples the value of k-point in z-direction, > for the scattering and tbtran runs are not equal to one and it has high > value for example A3~60. I think we have to have just one k-point in > transport direction as we have open boundary condition in this direction. > Yes, you are essentially correct.
When dealing with 2 electrodes which spans the full unit-cell in the transverse directions and the semi-infinite directions are parallel one need not have any k-points along the semi-infinite directions. However, remember that transiesta first performs a siesta calculation which estimates the ground-state density which is the input for transiesta. Thus the electronic structure comes from a fully periodic calculation and then subsequently the open-boundary conditions are applied. Thus, if the ground state electronic structure is more adequately described using a couple, or more, k-points along the semi-infinite directions, you may indeed add them. But, then please note the output of transiesta which automatically reduces the number of k-points to 1 along the semi-infinite direction. Lastly, one may envision a system where there is periodicity along the semi-infinite directions (with 1D electrodes, for instance), in this case k-points along the semi-infinite directions are required. So finally the requirement is ONLY; if there is periodicity in your device region after having removed your electrodes you SHOULD use k-points. > > If we have 3 steps as bellow to calculate the transmission > 1-transiesta <electrod.fdf > to calculate Hamiltonian and overlap matrix of electrods > > 2-transiesta <scat.fdf > to calculate density matrix of scattering region ] > > 3-tbtran <scat.fdf > to calculate transmission > > I think we should take A1*A2*A3 k-point for the electrode part as > electrodes are periodic in 3 dimensions and A3 should be large for example > A3=100 and A1 and A2 are like as standard DFT calculations. > for the second part we should take A1*A2*1 k-point as the system is open > in z-direction (A1 and A2 are same as electrode part). > Correct, with the additional considerations I have outlined above. > Finally for the tbtran run we need high k-point density in the periodic > directions and just 1 kpoint in the z direction for example B1*B2*1 (B1, B2 > > A1, A2). > > > Would you please correct me if I misunderstood. > For general 2-electrode setups as in the transiesta implementation pre 4.1 you are correct. > > > I really appreciate your answer. > > Best > Zara > > -- Kind regards Nick
