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6.12 Coupled-Cluster Methods

6.12.12 Examples

(May 21, 2025)

Example 6.30  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

Example 6.31  A job for single point CCSDT energy of water with (core orbitals frozen)

$molecule
0 1
O
H 1 R1
H 1 R1 2 A

R1=1.0
A=104.0
$end

$rem
   BASIS  =  cc-pVDZ
   METHOD  =  CCSDT
   N_FROZEN_CORE FC
$end

Example 6.32  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

Example 6.33  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

Example 6.34  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

Example 6.35  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

Example 6.36  A job evaluating the BWs-CC2 energy of formaldehyde with α=1

$molecule
0 1
C   0.0000      0.0000      0.0000
O   0.0000      0.0000     -1.2195
H   0.9391      0.0000      0.5422
H  -0.9391      0.0000      0.5422
$end

$rem
JOBTYPE             SP
METHOD              RIBWS2              ! activate RI-BWS2 driver
BASIS               DEF2-SVP
AUX_BASIS           RIMP2-DEF2-SVP      ! auxilliary basis is required
SYM_IGNORE          TRUE
SYMMETRY            FALSE
$end

$bws2
METHOD              BWS2                ! Use BW-s2 partition
EXC_METHOD          CC2                 ! Do a subsequent BWs-CC2 calculation
ALPHA               1000                ! a = 1.0
MAX_CYCLES          50
$end

Example 6.37  A job evaluating the BWs-CC2 energy of formaldehyde using the MPR-BWs2 partitioning with A0=1 and B0=-1.

$molecule
0 1
C   0.0000      0.0000      0.0000
O   0.0000      0.0000     -1.2195
H   0.9391      0.0000      0.5422
H  -0.9391      0.0000      0.5422
$end

$rem
JOBTYPE             SP
METHOD              RIBWS2              ! activate RI-BWS2 driver
BASIS               DEF2-SVP
AUX_BASIS           RIMP2-DEF2-SVP      ! auxilliary basis is required
SYM_IGNORE          TRUE
SYMMETRY            FALSE
$end

$bws2
METHOD              MPR-BWS2            ! Use MPR-BWs2 partition
EXC_METHOD          CC2                 ! Do a subsequent BWs-CC2 calculation
MPR_A0              1000                ! A_0 = 1.0
MPR_B0              -1000               ! B_0 = -1.0
MAX_CYCLES          50
$end