Point defects in diamond are responsible for a wide range of optoelectronic properties, making it crucial to engineer defect concentrations for novel applications. However, considering the plethora of defects in co-doped semiconducting and dielectric materials and the dependence of defect formation energies on heat treatment parameters, process-design based on an experimental trial and error approach is not an efficient strategy. This makes it necessary to explore computational pathways for predicting defect equilibria during heat treatments. By considering nitrogen, hydrogen, and silicon doped diamond, we have investigated the pressure dependence of defect formation energies and calculated the defect equilibria during heat treatment of diamond through abinitio calculations. We have plotted monolithic-Kroger-Vink diagrams for various defects, representing defect concentrations based on process parameters, such as temperature and partial pressure of gases used during heat treatments of diamond. The method demonstrated predicts the majority of experimental data, such as nitrogen aggregation path leading towards the formation of the B center, annealing of the B, H3, N3, and NVHx centers at ultra high temperatures, the thermal stability of the SiV center, and temperature dependence of NV concentration. We demonstrate the possibility of designing heat treatments for diamond and other semiconducting or dielectric materials through ab-initio modeling of defect equilibria.