7.12 Restricted Active Space Spin-Flip (RAS-SF) and Configuration Interaction (RAS-CI)

7.12.11 Examples

(May 16, 2021)

Example 7.122  Input for a RAS-2SF-CI calculation of three states of the DDMX tetraradical using RASCI1. The active space (RAS2) contains 4 electrons in the 4 singly occupied orbitals in the ROHF quintet reference. Natural orbital occupancies are requested.

$molecule
   0 5
   C      0.000000    0.000000    1.092150
   C     -1.222482    0.000000    0.303960
   C     -2.390248    0.000000    1.015958
   H     -2.344570    0.000000    2.095067
   H     -3.363161    0.000000    0.537932
   C     -1.215393    0.000000   -1.155471
   H     -2.150471    0.000000   -1.702536
   C      0.000000    0.000000   -1.769131
   C      1.215393    0.000000   -1.155471
   H      2.150471    0.000000   -1.702536
   C      1.222482    0.000000    0.303960
   C      2.390248    0.000000    1.015958
   H      2.344570    0.000000    2.095067
   H      3.363161    0.000000    0.537932
$end

$rem
   EXCHANGE        hf
   CORRELATION     rasci
   BASIS           6-31g
   UNRESTRICTED    false
   MEM_TOTAL       4000
   MEM_STATIC      100
   RAS_ROOTS       3
   RAS_ACT         4
   RAS_ELEC        4
   RAS_OCC         25
   RAS_SPIN_MULT   0
   RAS_NATORB      true
$end

View output

Example 7.123  Input for a RAS-2IP-CI calculation of triplet states of F2 molecule using the dianion closed shell F2-2 as the reference determinant. RASCI1 code is used

$molecule
   -2 1
   F
   F  1  1.4136
$end

$rem
   EXCHANGE        hf
   CORRELATION     rasci
   BASIS           cc-pVTZ
   MEM_TOTAL       4000
   MEM_STATIC      100
   RAS_ROOTS       2
   RAS_ACT         6
   RAS_ELEC        10
   RAS_OCC         4
   RAS_SPIN_MULT   3
$end

View output

Example 7.124  Input for a FCI/STO-3G calculation of water molecule expanding the RAS2 space to the entire molecular orbital set. RASCI code is used.

$molecule
   0 1
   O   0.000  0.000   0.120
   H  -0.762  0.000  -0.479
   H   0.762  0.000  -0.479
$end

$rem
   EXCHANGE        hf
   CORRELATION     rasci
   BASIS           sto-3g
   MEM_TOTAL       4000
   MEM_STATIC      100
   RAS_ROOTS       1
   RAS_ACT         7
   RAS_ELEC        10
   RAS_OCC         0
   RAS_SPIN_MULT   1
   RAS_DO_HOLE     false
   RAS_DO_PART     false
$end

View output

Example 7.125  Methylene single spin-flip calculation using RASCI2

$molecule
   0 3
   C     0.0000000    0.0000000    0.0000000
   H    -0.8611113    0.0000000    0.6986839
   H     0.8611113    0.0000000    0.6986839
$end

$rem
   EXCHANGE       HF
   CORRELATION    RASCI2
   BASIS          cc-pVDZ
   AUX_BASIS      rimp2-cc-pVDZ
   UNRESTRICTED   false
   RAS_ACT_OCC    1    ! # alpha electrons
   RAS_ACT_VIR    1    ! # virtuals in active space
   RAS_ACT_DIFF   0    ! # set to 1 for odd # of e-s
   RAS_N_ROOTS    4
   SET_ITER       25   ! number of iterations in RASCI
$end

View output

Example 7.126  Two methylene separated by 10 Å; double spin-flip calculation using RASCI2. Note that the S2 values for this case will not be uniquely defined at the triply-degenerate ground state.

$molecule
   0 5
   C     0.0000000     0.0000000    0.0000000
   H    -0.8611113     0.0000000    0.6986839
   H     0.8611113     0.0000000    0.6986839
   C     0.0000000    10.0000000    0.0000000
   H    -0.8611113    10.0000000    0.6986839
   H     0.8611113    10.0000000    0.6986839
$end

$rem
   EXCHANGE       HF
   CORRELATION    RASCI2
   BASIS          cc-pVDZ
   AUX_BASIS      rimp2-cc-pVDZ
   RAS_ACT_OCC    2    ! # alpha electrons
   RAS_ACT_VIR    2    ! # virtuals in active space
   RAS_ACT_DIFF   0    ! # set to 1 for odd # of e-s
   UNRESTRICTED   false
   RAS_N_ROOTS    8
   SET_ITER       25
$end

View output

Example 7.127  RASCI2 calculation of the nitrogen cation using double spin-flip.

$molecule
   1 6
   N
   N   1  4.5
$end

$rem
   EXCHANGE           HF
   CORRELATION        RASCI2
   BASIS              6-31G*
   AUX_BASIS          rimp2-VDZ
   RAS_ACT_OCC        3   ! # alpha electrons
   RAS_ACT_VIR        3   ! # virtuals in active space
   RAS_ACT_DIFF       1   ! # for odd # e-s, cation
   UNRESTRICTED       false
   N_FROZEN_CORE      2
   N_FROZEN_VIRTUAL   2
   RAS_N_ROOTS        8
   SET_ITER           25
$end

View output

Example 7.128  RAS(h,p)-1SF calculation of the nitrogen cation using librassf.

$molecule
   0 7
   N
   N   1   1.75
$end

$rem
   EXCHANGE            HF
   CORRELATION         RASCI2
   BASIS               cc-pvdz
   LIBRASSF            1
   RASSF_DELTA_ALPHA   1
   RASSF_DELTA_BETA    1
   RAS_N_ROOTS         4
   RAS_DO_HOLE         1
   RAS_DO_PART         1
   RAS_NATORB          0
$end

View output

Example 7.129  SOC calculation of HSiCl molecule using RASCI2 method with double spin-flip. No NTO analysis is requested within this example.

$molecule
   0 1
   Si    0.00000    0.00000    0.00000
   H     1.56100    0.00000    0.00000
   Cl   -0.45728    2.01271    0.00000
$end

$rem
   EXCHANGE          HF
   CORRELATION       RASCI2
   BASIS             cc-pVDZ
   AUX_BASIS         rimp2-cc-pVDZ
   UNRESTRICTED      false
   RAS_ACT_OCC       2    ! # alpha electrons
   RAS_ACT_VIR       2    ! # virtuals in active space
   RAS_ACT_DIFF      0    ! # set to 1 for odd # of e-s
   RAS_N_ROOTS       8
   SET_ITER          25
   N_FROZEN_CORE     fc
   N_FROZEN_VIRTUAL  0
   RAS_CALC_SOC      true
$end

View output

Example 7.130  SOC calculation followed by NTO analysis of acetophenone molecule using RASCI2 method with double spin-flip.

$molecule
   0 1
   C   -2.517371    0.513126    0.001828
   C   -1.316451   -0.371636    0.001013
   C   -1.553894   -1.827349    0.000191
   C   -2.806559   -2.314044   -0.001563
   C   -3.962422   -1.432985   -0.002120
   C   -3.757473   -0.015730    0.000047
   C   -0.030094    0.202242    0.001108
   C    1.208765   -0.658368   -0.000434
   O    0.079290    1.457055    0.003022
   H    2.079440   -0.009753   -0.004191
   H   -0.705807   -2.494690    0.000993
   H   -2.970202   -3.383004   -0.002372
   H   -4.958256   -1.847303   -0.003648
   H   -4.620034    0.636483    0.000372
   H   -2.340078    1.575881    0.003550
   H    1.252514   -1.299975    0.880472
   H    1.247817   -1.304378   -0.878269
$end

$rem
   EXCHANGE          HF
   CORRELATION       RASCI2
   BASIS             cc-pVDZ
   AUX_BASIS         rimp2-cc-pVDZ
   UNRESTRICTED      false
   RAS_ACT_OCC       2    ! # alpha electrons
   RAS_ACT_VIR       2    ! # virtuals in active space
   RAS_ACT_DIFF      0    ! # set to 1 for odd # of e-s
   RAS_N_ROOTS       4
   SET_ITER          25
   N_FROZEN_CORE     fc
   N_FROZEN_VIRTUAL  0
   RAS_CALC_SOC      true
   MOLDEN_FORMAT     true
   NTO_PAIRS         2
$end

View output