2018年11月16日 · FCIQMC-SCF: like CASSCF but rather than doing FCI on the CAS you do FCIQMC, which includes configurations with all possible levels of excitation, but only the most important configurations survive a Monte Carlo sampling process.

2016年5月3日 · CASSCF is quite similar to CI, in the sense that a full CI wavefunction is generated within the active space used in the CASSCF method. However, the CI method is a so-called ground state method, while the CASSCF method is multi-configurational.

2017年5月13日 · CASSCF mainly recovers the static correlation, but of course a small part of the dynamic correlation is recovered by the fact that the wave function is multi-configurational; we include the dynamic correlation between the active electrons, I suppose. $\endgroup$

2017年6月7日 · Doing a single CASSCF calculation with no "preparation" beforehand should force most programs to start with Hartree-Fock-like orbitals; this is the reference wavefunction $\Psi_0$. Hartree-Fock includes almost no static correlation to speak of, which can manifest in an incorrect ordering of the orbitals when compared to MOs that do have static ...

2017年11月4日 · I have a question about the CASSCF method. According to what I have read, it is easiest to build the CASSCF active space by selecting specific localized orbitals from a small-basis DFT or MP2 calculation. With near-minimal basis sets, it is easy to identify important active space orbitals visually (e.g., $\sigma$, $\sigma^*$, etc.)

2016年6月23日 · ORCA makes it easy to get started with CASSCF, and it has plenty of knobs, but it has a very slow integral engine, doesn't prevent you from doing stupid things like GAMESS, and more advanced features are poorly documented. The workflow described above (namely the plotting orbitals and rotating them) becomes very tedious as well, but that has ...

2018年6月24日 · The orbitals in CASSCF (or MCSCF in general) are optimized for a specific electronic state (= linear combination of CSFs) or a user-defined (weighted) state-average. If they would belong just to the largest CSF, they would be equal to the HF orbitals.

2019年4月26日 · Is see that SA-CASSCF is quite standard in the literature, even in cases when root-flipping wouldn't necessarily cause an issue, and I don't understand why making such compromise to obtain a single set of orbitals makes theoretical sense.

2017年1月18日 · To perform a CASSCF calculation in MOLCAS, you have to supply a "standard" SCF calculation, specifically the orbitals, in a manner that the CASSCF module of MOLCAS can read them and use them as the one-determinantal basis for the following CASSCF procedure.

2017年10月30日 · Use the checkpoint file obtained in step 1 and use CASSCF (provided I know the active space) to optimize the structure again and then use the scan keyword to map the PES by increasing the N-H bond distance in a different Gaussian job.