7

Start by looking at the Hamiltonian for a molecular system \begin{equation} \label{eq:coulomb_hamiltonian} \hat{H} = - \sum\limits_{α=1}^{ν} \frac{1}{2 m_{α}} \nabla_{α}^{2} - \sum\limits_{i=1}^{n} \frac{1}{2} \nabla_{i}^{2} - \sum\limits_{α=1}^{ν} \sum\limits_{i=1}^{n} \frac{Z_{α}}{r_{αi}} + \sum\limits_{α=1}^{ν} \sum\limits_{β > α} \...


6

According to the Gaussian Frequently Asked Questions: In general, a stationary point is found when one of two criteria is met for a point in an optimization calculation: All four values listed in the output are smaller than the indicated thresholds. The Maximum Force and RMS Force are two orders of magnitude smaller than the thresholds shown, ...


5

This is actually a lot simpler than I initially thought. I'll be using the same example as previously explained in How to obtain the radial probability distribution function from a quantum chemical calculation? My test setup has slightly changed since then, i.e. I've tried it with Gaussian 16 B.01 and Multiwfn 3.6.0 and it worked the same. We start the same ...


4

tldr - atomic partial charges can be non-intuitive Formal charges in a Lewis structure don't always match up with partial charge assignment methods. Typically, one wants 'accurate' partial charge models, for some definition of 'accurate' - but what that means can vary considerably. I explained some of this in a related question. While I haven't worked ...


2

I figured that I was using the wrong format, the detailed format of .SKF files is given here The correct extracted parameterization profile is given below:


2

Using ORCA and reverse engineering the calculation provided in the question (HF/STO-3G at a $\ce{H}$-$\ce{F}$ distance of 0.955464 Angstroem), I obtained the following output, to which I added the matrix product of the density and overlap matrices, dubbed the Mulliken Population Matrix. By comparing to the output of other programs, the reader can follow the ...


2

I recently realised that the STO-nG basis functions were fit to 1s/20/3d STOs of various exponents, instead of being fit to STOs of higher principal quantum numbers (such as 2s/3p orbitals etc.). If I understand what you are saying, this is incorrect (although feel free to clarify if I am not understanding the question). Here is the paper documenting STO-...


2

Has a Gaussian expansion of STOs of higher quantum numbers (for example, 2s or 3p STOs) been performed I am unaware of such fitting. Typically, basis sets using higher angular momenta (cc-pV$n$Z, def2-$n$ZVP, pc-$n$) are fitted on total energies or correlation energies. See https://www.basissetexchange.org/ for examples and references. Are there any GTO ...


1

This "experiment" is about determining bond dissociation energy. The general way to solve this isn't like calculating enthalpies of reaction, as I initially thought, but rather through calculating the energy of two CH3 radicals, and comparing it with ethane. As another user pointed out, this should be done with unrestricted Hartree Fock and with diffuse ...


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