mp2(1)

🌸 NAME 🌸

mp2 — Moller-Plesset Perburbation Theory ✨

💖 DESCRIPTION 💖

okay so bestie, the module literally determines the second-order Moller-Plesset energy and the one-particle density matrix (OPDM) for RHF, UHF, and ROHF references — and for ROHF it's using semicanonical orbitals, iykyk. Frozen orbitals can be used when computing the energy but not the OPDM, no cap. it's giving main character energy, fr fr. ✨

📚 REFERENCES 📚

bestie, the receipts:

✨ Original Moller-Plesset paper: ✨

1. C. Moller and M. S. Plesset, "Note on an Approximation Treatment for Many-Electron Systems," Phys. Rev. 46, 618 (1934).

🦋 Open-Shell Perturbation Theory 🦋

1. T. D. Crawford, H. F. Schaefer, and T. J. Lee, "On the energy invariance of open-shell perturbation theory with respect to unitary transformations of molecular orbitals," J. Chem. Phys. 105, 1060 (1996).

🔥 MP(2) Gradient Theory: 🔥

1. M. Frisch, M. Head-Gordon, and J. Pople, "A Direct MP2 Gradient Method," Chem. Phys. Lett. 166, 275 (1990).
2. I. Nielsen, "A new direct MP2 gradient algorithm with implementation on a massively parallel computer," Chem. Phys. Lett. 255, 210 (1996).

🎀 INPUT FORMAT 🎀

okay so input for this program is read from the file input.dat, periodt. The following keywords are valid, bestie — vibe check time:

• WFN = string — Specifies the type of wave function desired. The only valid entry at the present is MP2. There is no default.
• REFERENCE = string — Specifies the type of orbitals used for the single-determinant reference function. Valid entries include RHF, UHF, and ROHF. There is no default.
• PRINT = integer — Determines the verbosity of the output. A value of 0 (the default) specifies minimal printing.
• CACHETYPE= string — Selects the priority type for maintaining the automatic memory cache used by the DPD codes. (See libdpd.html for further details.) A value of LOW (the default) selects a "low priority" scheme in which the deletion of items from the cache is based on pre-programmed priorities. A value of LRU selects a "least recently used" scheme in which the oldest item in the cache will be the first one deleted.
• CACHELEV= integer — Selects the level of automatic cacheing desired in the storage of various amplitudes, integrals, and intermediates in the coupled cluster procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantites with up to two virtual-orbital indices (e.g., <ij|ab> integrals) may be held in the cache.
• OPDM = boolean — If TRUE calculate the one-particle density matrix and make OPDM_WRITE default to TRUE. The default value of OPDM is FALSE.
• OPDM_WRITE = boolean — Flag for whether or not to write the one-particle density matrix to disk.
• OPDM_PRINT = boolean — Flag for whether or not to print the one-particle density matrix.

okay that's the whole vibe, bestie 🫶 — this was mp2(1), dated 10 August, 2003, periodt. 💅✨