# sc::MBPT2_R12 Class Reference

The MBPT2_R12 class implements several linear R12 second-order perturbation theory methods. More...

`#include <mbptr12.h>`

Inheritance diagram for sc::MBPT2_R12:

List of all members.

## Public Member Functions
| MBPT2_R12 (StateIn &)
| MBPT2_R12 (const Ref< KeyVal > &)
| The KeyVal constructor.
void | save_data_state (StateOut &)
| Save the base classes (with save_data_state) and the members in the same order that the StateIn CTOR initializes them.
Ref< GaussianBasisSet > | aux_basis () const
Ref< GaussianBasisSet > | vir_basis () const
bool | gbc () const
bool | ebc () const
LinearR12::ABSMethod | abs_method () const
LinearR12::StandardApproximation | stdapprox () const
bool | spinadapted () const
R12IntEvalInfo::StoreMethod | r12ints_method () const
const std::string & | r12ints_file () const
double | corr_energy ()
double | r12_corr_energy ()
RefSymmSCMatrix | density ()
| Returns the SO density.
void | obsolete ()
| Marks all results as being out of date.
int | gradient_implemented () const
int | value_implemented () const
| Information about the availability of values, gradients, and hessians.
void | print (std::ostream &o=ExEnv::out0()) const
| Print information about the object.
## Protected Member Functions
void | compute ()
| Recompute at least the results that have compute true and are not already computed.

## Detailed Description

The MBPT2_R12 class implements several linear R12 second-order perturbation theory methods.

## Constructor & Destructor Documentation

sc::MBPT2_R12::MBPT2_R12 | ( | const Ref< KeyVal > & |  | ) |

The KeyVal constructor.

`gbc`

  This boolean specifies whether Generalized Brillouin Condition (GBC) is assumed to hold. The default is "true". This keyword is only valid if stdapprox=A'. The effect of setting this keyword to true is rather small -- hence it is not recommended to use this keyword.

`ebc`

  This boolean specifies whether Extended Brillouin Condition (EBC) is assumed to hold. The default is "true". This keyword is only valid if stdapprox=A'. The effect of setting this keyword to true is rather small -- hence it is not recommended to use this keyword.

`stdapprox`

  This gives a string that must take on one of the values below. The default is A'.

  `A`

    Use second order Møller-Plesset perturbation theory with linear R12 terms in standard approximation A (MP2-R12/A). Only energies can be computed with the MP2-R12/A method.

  `A'`

    Use second order Møller-Plesset perturbation theory with linear R12 terms in standard approximation A' (MP2-R12/A'). This will cause MP2-R12/A energies to be computed also. Only energies can be computed with the MP2-R12/A' method.

  `B`

    Use second order Møller-Plesset perturbation theory with linear R12 terms in standard approximation B. This method is not implemented yet.

`spinadapted`

  This boolean specifies whether to compute spin-adapted or spin-orbital pair energies. Default is to compute spin-adapted energies.

`aux_basis`

  This specifies the auxiliary basis to be used for the resolution of the identity. Default is to use the same basis as for the orbital expansion.

`vir_basis`

  This specifies the basis to be used for the virtual orbitals. Default is to use the same basis as for the orbital expansion.

`include_mp1`

  This specifies whether to compute MP1 correction to the MP2 and MP2-R12 energies. This option only has effect if vir_basis is not the same as basis. MP1 correction is a perturbative estimate of the difference between the HF energy computed in vir_basis and basis. Usually, it is a very poor estimate -- therefore this keyword should be avoided by non-experts. Default is false.

`abs_method`

  This string specifies whether the old ABS method, introduced by Klopper and Samson, or the new ABS variant, CABS, introduced by Valeev, should be used. Valid values are "ABS" (Klopper and Samson), "ABS+", "CABS", and "CABS+", where the "+" labels a method where the union of OBS and ABS is used to construct the RI basis. The default is "ABS". The default in 2.3.0 and later will be "CABS+".

`lindep_tol`

  The tolerance used to detect linearly dependent basis functions in the RI basis set. The precise meaning depends on the orthogonalization method. The default value is 1e-8.

`r12ints`

  This specifies how to store transformed MO integrals. Valid values are:

  `mem-posix`

    Store integrals in memory for single-pass situations and in a binary file on task 0's node using POSIX I/O for multipass situations. `posix` is usually less efficient than `mpi` for distributed parallel multipass runs since the I/O is performed by one task only. However, this method is guaranteed to work in all types of environments, hence `mem-posix` is the default.

  `posix`

    Store integrals in a binary file on task 0's node using POSIX I/O. This method is different from `mem-posix` in that it forces the integrals out to disk even if they could be stored in memory. `posix` should only be used for benchmarking and testing purposes.

  `mem-mpi`

    Store integrals in memory for single-pass situations and in a binary file using MPI-I/O for multipass situations. This method assumes the availability of MPI-I/O. `mem-mpi` is the preferred choice in distributed environments which have MPI-I/O available.

  `mpi`

    Store integrals in a binary file using MPI-I/O. This method is different from `mem-mpi` in that it forces the integrals out to disk even if they could be stored in memory. `mpi` should only be used for benchmarking and testing purposes.

  `mem`

    Store integrals in memory. Can only be used with single-pass transformations for MP2-R12/A and MP2-R12/A' methods. This method should only be used for testing purposes.

  If `r12ints` is not specified, then `mem-posix` method will be used. If user wishes to use MPI-I/O, pending its availability, for higher parallel efficiency, `r12ints` should be explicitly set to `mem-mpi`.

`r12ints_file`

  This specifies the prefix for the transformed MO integrals file if `r12ints` is set to `posix`, `mpi`, `mem-posix` or `mem-mpi` is used. Default is "./<i>inputbasename</i>.r12ints", where inputbasename is the name of the input file without ".in". If MPI-I/O is used then it is user's responsibility to ensure that the file resides on a file system that supports MPI-I/O.

`twopdm_grid_aa`

  This optional keyword specifies a TwoBodyGrid object which to use for coordinates at which to compute alpha-alpha part of 2-PDM.

`twopdm_grid_ab`

  This optional keyword specifies a TwoBodyGrid object which to use for coordinates at which to compute alpha-beta part of 2-PDM.

## Member Function Documentation

void sc::MBPT2_R12::compute | ( |  | ) | `[protected, virtual]`

Recompute at least the results that have compute true and are not already computed.

This should only be called by Result's members.

Reimplemented from sc::MBPT2.

void sc::MBPT2_R12::obsolete | ( |  | ) | `[virtual]`

Marks all results as being out of date.

Any subsequent access to results will cause Compute::compute() to be called.

Reimplemented from sc::MBPT2.

void sc::MBPT2_R12::save_data_state | ( | StateOut & |  | ) | `[virtual]`

Save the base classes (with save_data_state) and the members in the same order that the StateIn CTOR initializes them.

This must be implemented by the derived class if the class has data.

Reimplemented from sc::MBPT2.

int sc::MBPT2_R12::value_implemented | ( |  | ) | const`[virtual]`

Information about the availability of values, gradients, and hessians.

Reimplemented from sc::MBPT2.

The documentation for this class was generated from the following file:

- mbptr12.h