The silicon anisotropic wet chemical etching technique is widely employed for fabricating various microelectromechanical system structures for advantages such as simple etching equipment and its capability to fabricate special microstructures. In this paper, we consider one of the most frequently used equations of atomistic model of simulation of anisotropic wet etching. Then using a trial and error method we solve the mentioned equations and derive a new equation for calculating the microscopic etch rates of some surface atoms for a new range of concentrations and temperatures. Furthermore, a new equation is presented for the calculation of the microscopic activation energies for some typical surface atoms and a new comparison of activation energies between some atoms is made dividing atoms into three categories. This classification makes it easier to study microscopic etch rates and activation energies of other atoms. The results demonstrate a good agreement with the experimental results.