Fast corrections to the generalized Kadanoff-Baym ansatz

A quantum kinetic equation for the density matrix is derived from nonequilibrium Green functions using the generalized Kadanoff-Baym ansatz and corrections beyond. The Markovian reconstruction of the Green function and the quasistationary approximation are used to approximate the corrections, making their implementation in numerical simulations faster. On electron tunneling under conditions when the prediction of the uncorrected kinetic equation seriously departs from the exact solution, we show that the corrections reduce the error by an order of magnitude.