Basisuppsättningar

Basisuppsättningar, often translated as "basis sets" in English, are collections of mathematical functions used in quantum chemistry to approximate the electronic wave functions of atoms and molecules. These functions, typically Gaussian-type orbitals (GTOs), serve as the building blocks for constructing molecular orbitals. The accuracy of computational chemistry calculations, such as those performed using the Hartree-Fock or density functional theory methods, is directly dependent on the quality and size of the basis set employed.

A basis set is characterized by the number and type of atomic orbitals included. Smaller basis sets, like STO-3G, are computationally inexpensive but provide less accurate results. Larger basis sets, such as those with polarization and diffuse functions (e.g., Pople basis sets like 6-311++G(d,p) or correlation-consistent basis sets like cc-pV5Z), offer higher accuracy by better describing the electron distribution, particularly in regions of low electron density or where electrons are more delocalized. The choice of basis set involves a trade-off between computational cost and desired accuracy. For routine calculations, a moderately sized basis set is often sufficient, while high-precision studies may necessitate larger, more complex basis sets.