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title: TranSiesta details
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This part of the documentation details the TranSiesta implementation.
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TranSiesta is a solution method that calculates the (non) equilibrium density
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by using open boundary conditions.
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Currently TranSiesta does not implement non-collinear, nor spin-orbit calculations.
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TranSiesta calculates the density matrix using the following procedure:
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1. Setup all parameters that are to be used in the TranSiesta calculation.
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This is mainly the electrode Hamiltonian and self-energy calculations.
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The self-energies require the coupling along the semi-infinite direction
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to only couple to nearest neighbours, see [[m_ts_init:ts_init]].
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2. Calculate an initial guess of the Hamiltonian and Fermi-level using
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any regular Siesta method, see [[compute_dm]].
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3. When solving the Hartree potential it is vital that the boundary is
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"fixed" such that the potential is kept constant where the electrode
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are fixed. This is because the open boundary couples to a constant
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potential, the electrodes.
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This boundary is chosen as the electrode that has the largest cross
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section along the semi-infinite direction, see [[m_ts_hartree:ts_hratree_fix]].
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4. Start the Green function method. In the
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TranSiesta SCF the electrode self-energies are taken from the TSGF*
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files and used to calculate the device Green function, see [[m_transiesta:transiesta]].
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5. Mix the Hamiltonian or density matrix as in regular Siesta calculations.
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6. Repeat step 3, 4 and 5.
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Currently, the TranSiesta implemention can calculate the Green function
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using 3 different methods:
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1. The full Green function [[m_ts_fullg:ts_fullg]]/[[m_ts_fullk:ts_fullk]]
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2. MUMPS library for sparse inversion [[m_ts_mumpsg:ts_mumpsg]]/[[m_ts_mumpsk:ts_mumpsk]]
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3. Block tri diagonal inversion [[m_ts_trig:ts_trig]]/[[m_ts_trik:ts_trik]]
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By far, the block tri diagonal inversion is the fastest and least memory
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Docs/developer/ford-pages/transiesta/index.md
