---
name: "mp2r12"
section: "1"
platform: "linux"
package: "psi3"
version: "3.4.0-6+b3"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/mp2r12"
---

# mp2r12(1)

**NAME**      **mp2r12 - calculates the MP2-R12 energy in standard approximation A**  **for closed-shell systems.**

**DESCRIPTION**      **The program** **mp2r12**      **determines the linear-R12 second-order Moller-Plesset energy** **for closed-shell systems.** **Input integrals must come from the restricted transformation available in** **the**  **TRANSQT**      **program.  Frozen orbitals are not allowed, as the basis sets used in linear-R12** **computations employ basis sets with more than enough flexibility**  **to describe core-correlation effects correctly.**

**REFERENCES**

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).**

```
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)
```

```
output.dat
```

**INPUT OPTIONS**

**mp2r12**      **has the following options:**

**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.**

**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.**