# EXCHANGE_CORRECTION

Parameters influencing exchange corrections to RPA. No gradients available. [Edit on GitHub]

## Keywords

- SECTION_PARAMETERS

- BLOCK_SIZE

- USE_HFX_IMPLEMENTATION

## Keyword descriptions

SECTION_PARAMETERS: enum = NONE

  Usage: &EXCHANGE_CORRECTION AXK

  Valid values:

  - `NONE` Apply no exchange correction.

  - `AXK` Apply Approximate eXchange Kernel (AXK) correction.

  - `SOSEX` Apply Second Order Screened eXchange (SOSEX) correction.

  Choose the kind of exchange correction. [Edit on GitHub]

BLOCK_SIZE: integer = 1

  Usage: BLOCK_SIZE 1

  Choose the block size of the contraction step. Larger block sizes improve performance but require more memory (quadratically!, number of stored elements: \(o^2\cdot N_B^2\)). Nonpositive numbers turn off blocking. [Edit on GitHub]

USE_HFX_IMPLEMENTATION: logical = F

  Lone keyword: `T`

  Usage: USE_HFX_IMPLEMENTATION T

  Use a HF-based implementation with RI_RPA%HF section. Recommended for large systems. [Edit on GitHub]