Multireference configuration interaction (MRCI)

Description

Fully internally contracted multireference configuration interactions up to the two-electron excitation (MRCISD). This is implemented with the automatical code generator SMITH3. By default, the Davidson corrected (+Q) energy is also printed.

Title: smith, method: mrci

Prerequisites

A reference wavefunction generated by a HF or CASSCF calculation.

Keywords

SMITH keywords

The default values are recommended unless mentioned otherwise.

thresh

Description: Convergence threshold.
Datatype: double precision
Default: 1.0e-8 (gradient) 1.0e-6 (otherwise)

thresh_overlap

Description: Overlap threshold.
Datatype: double precision
Default: 1.0e-9

frozen

Description: Freeze core orbitals.
Datatype: bool
Default: true

ncore

Description: Number of frozen core orbitals.
Datatype: int
Default: If frozen is true, subvalence orbitals are frozen. If false, zero.

nfrozenvirt

Description: Number of frozen virtual orbitals.
Datatype: int
Default: 0

maxiter

Description: Maximum number of iterations in MRCI calculations.
Datatype: int
Default: 50

maxtile

Description: Maximum number of orbitals in a single data tile used in SMITH3.
Datatype: int
Default: 10

Example

{ "bagel" : [

{
  "title" : "molecule",
  "basis" : "svp",
  "df_basis" : "svp-jkfit",
  "angstrom" : true,
  "geometry" : [
     { "atom" : "O",  "xyz" : [   -0.000000,     -0.000000,      1.210000]},
     { "atom" : "O",  "xyz" : [   -0.000000,     -0.000000,      0.000000]}
  ]
},

{
  "title" : "casscf",
  "nclosed" : 7,
  "nact" : 2
},

{
  "title" : "smith",
  "method" : "mrci"
}

]}

from which one obtains

* freezing 2 orbitals
* XMS rotation is only appropriate for CASPT2, and will not be used with mrci
   - MO integral evaluation                    0.01
- linear dependency detected:    3 /    4    min eigenvalue:     0.0000e+00    max eigenvalue:     0.0000e+00
- linear dependency detected:    3 /    4    min eigenvalue:    -3.9968e-15    max eigenvalue:    -1.1102e-15
- linear dependency detected:    4 /    8    min eigenvalue:    -1.0380e-15    max eigenvalue:     2.9134e-15
- linear dependency detected:    6 /    8    min eigenvalue:     0.0000e+00    max eigenvalue:     0.0000e+00
- linear dependency detected:    6 /    8    min eigenvalue:    -1.2102e-15    max eigenvalue:     9.1101e-16
   - RDM + denominator evaluation              0.00

* Zeroth order energy : state  0       -0.4388085255

  ---- iteration ----

    0   0  -149.74880423     0.00455295      0.06
    1   0  -149.76848791     0.00088584      0.06
    2   0  -149.76925804     0.00021094      0.06
    3   0  -149.76932381     0.00006783      0.07
    4   0  -149.76932906     0.00001772      0.07
    5   0  -149.76932932     0.00000337      0.06
    6   0  -149.76932933     0.00000065      0.07

  -------------------

   - MRCI energy evaluation                    0.46

    0   0  -149.80276480     0.00000000      0.00

   - MRCI+Q energy evaluation                  0.00

* METHOD: SMITH                                0.48

References

Fully internally contracted MRCI itself is not particularly new.

BAGEL References

Description of Reference Reference
SMITH3 M. K. MacLeod and T. Shiozaki, J. Chem. Phys. 142, 010507 (2015)
Relativistic extension T. Shiozaki and W. Mizukami, J. Chem. Theory Comput. 11, 4733 (2015)

General References

Description of Reference Reference
Fully internally contracted MRCI H.-J. Werner and E.-A. Reinsch, J. Chem. Phys. 76, 3144 (1982)
Modern implementation M. Saitow, Y. Kurashige, and T. Yanai, J. Chem. Phys. 139, 044118 (2013)