There have been many discoveries from observations of accreting neutron stars in X-ray binaries. Many of the observed phenomena such as superbursts or the cooling of quasi-persistent transients during their quiescent state are affected by the thermal properties and the composition of the crust. To model the nuclear energy release and crust composition, we build up a first complete network with pycnonuclear fusion. We run a consistent nuclear reaction network that follows the evolution of an accreted fluid element from the atmosphere down to the inner crust. We take into account a majority of the most important nuclear processes including electron capture, neutron capture, neutron emissions, $beta decay, and pycnonuclear fusion reactions. The result of the model shows that there is nuclear reaction path splitting in the crust of accreting neutron stars due to the usage of finite electron capture rates. The pycnonuclear fusion reactions can occur at a shallower depth than previously thought. The composition deep inside the inner crust is mainly 40Mg, independent of the initial composition of the ashes of the outer crust. The inner crust is found to be very pure no matter what the initial abundance of the ashes is in the outer crust. The neutron drip locates at a higher density in our model. In general, the nuclear reaction path and the heat energy generation in the inner crust are significantly different from the previous work.
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