Light atoms, such as oxygen, are treated with the 6-311G** basis sets, and heavy atoms, like tin (Sn), are treated with SDD (Stuttgart/Dresden) basis sets. A density functional theory (DFT) with a B3LYP hybrid functional calculation needs to be done to work out the geometrical and electronic properties, such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and the energy gap, as well as the thermodynamic properties, such as Gibbs free energy, enthalpy, entropy, and heat capacity of the tin dioxide (SnO₂) pyramid nanocluster structure as a function of the number of oxygen atoms. These theoretical calculations were performed using Gaussian 09W, while the geometry was visualized using Gaussian View 05. It was found that the SnO₂ pyramid nanocluster energy gap in the beginning increased with the increase of the oxygen atoms and reached a maximum at Sn₁₀O₁₆, then dropped to a minimum value at 2.55 eV for Sn₁₀O₁₇. The Gibbs free energy and enthalpy values became more negative, indicating that the reaction was exergonic.