  In the paper a new method to solve the tree-dimensional reference interaction
site model (3DRISM) integral equations is proposed. The algorithm uses the
multi-grid technique which allows to decrease the computational expanses.
3DRISM calculations for aqueous solutions of four compounds (argon, water,
methane, methanol) on the different grids are performed in order to determine a
dependence of the computational error on the parameters of the grid. It is
shown that calculations on the grid with the step 0.05\Angstr and buffer
8\Angstr give the error of solvation free energy calculations less than 0.3
kcal/mol which is comparable to the accuracy of the experimental measurements.
The performance of the algorithm is tested. It is shown that the proposed
algorithm is in average more than 12 times faster than the standard Picard
direct iteration method.
