MP2R12(1)

💖 mp2r12 — bestie edition ✨

okay so real quick, before we get into it: this is the page for mp2r12, one of the PSI COMMANDS FOR UNIX USERS. she lives in the Psi Release 2.0 era and honestly? she's iconic. let's go 🦋

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✨ NAME ✨

mp2r12 — calculates the MP2-R12 energy in standard approximation A for closed-shell systems. that's the whole vibe. 💅

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🌸 DESCRIPTION 🌸

so what does mp2r12 actually do, you ask? bestie. she determines the linear-R12 second-order Moller-Plesset energy for closed-shell systems. that's the main character job right there. 👑

now, the deets:

• your input integrals must come from the restricted transformation available in the TRANSQT program. no substitutions, no shortcuts, she will not accept your homemade integrals. 🚫
• frozen orbitals are not allowed. periodt. why? because the basis sets used in linear-R12 computations employ basis sets with more than enough flexibility to describe core-correlation effects correctly. she's got range, she doesn't need to freeze anything. ✨

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📚 REFERENCES 📚

if you wanna cite her (and you should, she ate), here's the reading list:

Moller-Plesset original paper:

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

Linear R12 theory formulation:

2. W. Kutzelnigg and W. Klopper, "Wave functions with terms linear in the interelectronic coordinates to take care of the correlation cusp. I. General Theory", J. Chem. Phys., 94, 1985(1991).

MP2-R12/A programmable expressions:

3. W. Klopper, "Limiting values for Moller-Plesset second-order correlation energies of polyatomic systems: A benchmark study on Ne, HF, H2O, N2, and He...He", J. Chem. Phys., 102, 6168(1995).

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🎀 FILES REQUIRED 🎀

she needs these. no FILE, no energy. simple as that:

input.dat
FILE30
FILE72        (electron repulsion integrals, produced by transqt)
FILE79        (integrals of r12 operator, produced by transqt)
FILE80        (integrals of [r12,T2] operator, produced by transqt)

ngl, the transqt ones are non-negotiable — FILE72, FILE79 and FILE80 all gotta be produced by transqt. 🫶

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🌈 FILES GENERATED 🌈

she makes you exactly one thing and honestly it's the one you wanted:

output.dat

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💅 INPUT OPTIONS 💅

mp2r12 has the following options. one bullet per option, we keep it cute, we keep it complete:

• PRINT_LVL = integer — Determines the verbosity of the printing information. A print value of 0 gives minimal information, while 5 gives debugging information (do NOT use print levels above 3 for more than 20 basis functions). The default is 0.

⚠️ for real, do not be out here running print levels above 3 with more than 20 basis functions. she said what she said. 💀

• TOLERANCE = integer — This gives the exponent of the cutoff value for the elimination of two-electron integrals from the list of those on disk. The default is 14, giving a cutoff of 1e-14.
• FROZEN_DOCC = int_array — Number of frozen doubly-occupied orbitals in each symmetry block. Default is a vector of zeroes.
• FROZEN_UOCC = int_array — Number of frozen unoccupied orbitals in each symmetry block. Default is a vector of zeroes.
• C_LIMIT = boolean — Instead of using variationally optimized C-coefficients, use limiting values (1/2 for singlet pairs, 1/4 for triplet pairs). Default is false.

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okay that's the whole page bestie, you're officially fluent in mp2r12. 🧚💜

Psi Release 2.0 girlies, this one was last changed on 06 August, 1999 — yes she's vintage, yes she still slays, and the copyright/license energy stays exactly as the original page had it. mwah. 💋 🎀🌸🦋✨