# Møller-Plesset Perturbation Theory

Møller-Plesset Perturbation Theory (MPPT) is a widely used method in quantum chemistry to account for electron correlation effects in many-body systems. It is based on perturbation theory and provides a systematic way to improve upon the Hartree-Fock approximation.

## Available Møller-Plesset Tasks

| Task                                            | Description                                                                    |
|-------------------------------------------------|--------------------------------------------------------------------------------|
| [`MP2`](./../general_sections/jobs.md#MP2)       | Second-order Møller–Plesset perturbation theory.                               |
| [`UMP2`](./../general_sections/jobs.md#UMP2)     | Unrestricted MP2; allows for spin-contaminated open-shell reference states.    |
| [`MP3`](./../general_sections/jobs.md#MP3)       | Third-order Møller–Plesset perturbation theory.                                |
| [`MP4SDQ`](./../general_sections/jobs.md#MP4SDQ) | Fourth-order MP including only Singles, Doubles, and Quadruples contributions. |
| [`MP4`](./../general_sections/jobs.md#MP4)       | Full fourth-order Møller–Plesset perturbation theory.                          |

## General Keywords for MPPT Tasks

| `frozencore` <a id="frozencore"></a> | |
|----------------|------------------------------------------------------------|
| **Description** | Enables freezing of core orbitals to reduce computational cost. |
| **Type**        | bool |
| **Default**     | False |