Simulation of chemical reactions and dust destruction in protoplanetary accretion disks.

This paper considers the gas phase chemistry in a protoplanetary accretion disk, especially the chemistry initiated in the gas phase by destruction of dust close to the central star. Slow radial particle transport moves gas and dust from the cold outer parts of a protoplanetary accretion disk into its warm central part where chemical reactions in the gas phase are activated. At the same time gases frozen on the surface of dust grains are vaporized and later the dust grains themselves are vaporized or destroyed by chemical surface reactions. These processes initiate a rich chemistry in the protoplanetary accretion disk. The simulation of chemical reactions, as in the case of an accretion disk, mostly leads to a large and stiff system of differential or differential-algebraic equations. For the integration of such systems implicit methods are required. We present an efficient BDF-method and give a detailed description of the error and stepsize control and the strategies to minimize the numerical effort of the linear algebra problems. Typical applications for chemical processes (chemistry and dust destruction) in an accretion disk are treated with this method. The corresponding code DAESOL turned out to be more robust and much faster than the more conventional code used first. Some results for the chemistry in a protoplanetary accretion disk are briefly discussed.