6.10 Coupled-Cluster Methods

6.10.9 Examples

(June 30, 2021)

Example 6.26  A series of jobs evaluating the correlation energy (with core orbitals frozen) of the ground state of the NH2 radical with three methods of coupled-cluster singles and doubles type: CCSD itself, CC2, OD, and QCCD.

$molecule
   0  2
   N
   H1  N  1.02805
   H2  N  1.02805  H1  103.34
$end

$rem
   METHOD          ccsd
   BASIS           6-31g*
   N_FROZEN_CORE   fc
$end

@@@

$molecule
   read
$end

$rem
   METHOD          cc2
   BASIS           6-31g*
   N_FROZEN_CORE   fc
$end

@@@

$molecule
   read
$end

$rem
   METHOD          od
   BASIS           6-31g*
   N_FROZEN_CORE   fc
$end

@@@

$molecule
   read
$end

$rem
   METHOD          qccd
   BASIS           6-31g*
   N_FROZEN_CORE   fc
$end

View output

Example 6.27  A job evaluating CCSD energy of water using RI-CCSD

$molecule
  0 1
  O
  H1 O OH
  H2 O OH H1 HOH

  OH  = 0.947
  HOH = 105.5
$end

$rem
   METHOD          ccsd
   BASIS           aug-cc-pvdz
   AUX_BASIS       rimp2-aug-cc-pvdz
$end

View output

Example 6.28  A job evaluating the RI-CC2 energy of water

$molecule
  0 1
  O
  H1 O OH
  H2 O OH H1 HOH

  OH  = 0.947
  HOH = 105.5
$end

$rem
   METHOD          cc2
   BASIS           aug-cc-pvdz
   AUX_BASIS       rimp2-aug-cc-pvdz
$end

View output

Example 6.29  A job evaluating CCSD energy of water using CD-CCSD (tolerance = 10-3)

$molecule
  0 1
  O
  H1 O OH
  H2 O OH H1 HOH

  OH  = 0.947
  HOH = 105.5
$end

$rem
   METHOD          ccsd
   BASIS           aug-cc-pvdz
   CHOLESKY_TOL    3
$end

View output

Example 6.30  A job evaluating CCSD energy of water using CD-CCSD (tolerance = 10-3) with FNO

$molecule
   0 1
   O
   H1 O OH
   H2 O OH H1 HOH

   OH  = 0.947
   HOH = 105.5
$end

$rem
   METHOD          ccsd
   BASIS           aug-cc-pvdz
   CHOLESKY_TOL    3
   CC_FNO_THRESH   9950
$end

View output