Molcas Forum

stratis

Member

Registered: 2022-05-20

Posts: 5

Contraction coefficients relation with primitive coefficients

Hello, at the end of each calculation I get a log file with information about the basis set used for the simulation and more specifically the exponents and contraction coefficients used for the primitive functions. My first question is in what units are the exponents expressed in, a) inverse Angstroms, b) inverse atomic units, or c) some other unit? My second question has to do with the contraction coefficients. From a quick search on Wikipedia (STO-nG) it shows that the primitive functions have a coefficient in front of them which is always the same. I call these coefficients in front of the primitive functions the primitive coefficients. Do the contraction coefficients that the program outputs contain the primitive coefficients in them or does the program calculate the corresponding primitive coefficients for each atomic orbital. Essentially, if Ψ^{MO} = \sum_i c_i * Φ^{AO}, and Φ^{MO}_i = \sum_k d_k * χ_k, where Ψ^{MO} is the molecular orbital, Φ^{AO} is the atomic orbital, and χ is the primitive function, do the contraction coefficients 'c_i' contain the primitive coefficients 'd_k' or not? Lastly, are the primitive coefficients the same for every basis set that uses Gaussian type primitives?