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# Interface Composite

This interface performs multiple calculations on the system using different methods. The results are then combined according to an user-defined formula. It is possible to work with both total; energy and its components.

## Keywords

- composite_method_names List of method names used to identify them in the input and in the equation.
- composite_equation

## Input

Each calculation should be specified in the input in a subsection calculation_*method_name*. The equation uses ruby syntax. Results of the calculations are accessible in variables named with the method name. These variables are hashes containing all the energy components (index is symbol corresponding to the component name). The total energy can be accessed as *method_name*[:energy]

## Example

Here is sample input for MP2/CBS extrapolation (Halkier et al. 1998) with CCSD(T) correction in smaller basis set.

```
interface: composite
charge: 0
composite_method_names:
- mp2t
- mp2q
- cc
composite_equation: "
mp2q[:scf_energy] +
(3**3 * mp2t[:mp2_corr_energy] - 4**3 * mp2q[:mp2_corr_energy])/(3**3 - 4**3) +
(cc[:ccsdt_corr_energy] - cc[:mp2_corr_energy])"
calculation_mp2t:
interface: molpro
method: mp2
density_fitting: yes
basisset: aug-cc-pVTZ
calculation_mp2q:
interface: molpro
method: mp2
density_fitting: yes
basisset: aug-cc-pVQZ
calculation_cc:
interface: molpro
method: ccsdt
basisset: aug-cc-pVDZ
```