6.21 Adaptive Sampling Configuration Interaction Method

6.21.3 ASCI Job Control

(May 16, 2021)

Active space specification and convergence details are controlled by the $rem variables described in Section 6.19.3. During the course of an ASCI calculation, a file named wf_data is created in the scratch directory containing information on the determinants and weights in the ASCI wavefunction.

ASCI_DIAG
       Specifies the diagonalization procedure.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       1 Davidson solver 2 Eigen sparse matrix solver
RECOMMENDATION:
       Use 2 for best trade-off of speed and memory usage. If memory usage becomes to great, switch to 1.

ASCI_NDETS
       Specifies the number of determinants to include in the ASCI wavefunction.
TYPE:
       INTEGER
DEFAULT:
       0
OPTIONS:
       N for a wavefunction with N determinants
RECOMMENDATION:
       Typical ASCI expansions range from 50,000 to 2,000,000 determinants depending on active space size, complexity of problem, and desired accuracy

ASCI_CDETS
       Specifies the number of determinants to search over during ASCI wavefunction growth steps.
TYPE:
       INTEGER
DEFAULT:
       -5
OPTIONS:
       N>0 search from the top N determinants N<0 search from the top determinants whose cumulative weight in the wavefunction corresponds to 1-2N
RECOMMENDATION:
       Using a dynamically determined value (N<0) gives better results.

ASCI_USE_NAT_ORBS
       Specifies whether rotation to a natural orbital basis should be carried out between growth steps.
TYPE:
       BOOLEAN
DEFAULT:
       TRUE
OPTIONS:
       TRUE rotate to a natural orbital basis between growth wavefunction growth steps FALSE do not rotate to a natural orbital basis
RECOMMENDATION:
       Natural orbital rotations significantly improve the compactness and therefore accuracy of the ASCI wavefunction.

ASCI_DAVIDSON_GUESS
       Specifies the truncated CI guess used for ASCI’s Davidson solver.
TYPE:
       INTEGER
DEFAULT:
       2
OPTIONS:
       N Order of the truncated CI to solve explicitly ASCI Davidson guess.
RECOMMENDATION:
       Accurate excited states and rapid convergence of the ground state benefit from a good zero-order guess for the low energy spectrum. The default is often sufficient.

ASCI_SKIP_PT2
       Specifies whether ASCI PT2 correction should be calculated.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       FALSE compute ASCI PT2 contribution TRUE do not compute ASCI PT2 contribution
RECOMMENDATION:
       The PT2 correction is essential to obtaining converged ASCI energies.

ASCI_RESTART
       Specifies whether to initialize the ASCI wavefunction with the wf_data file.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE read CI coefficients from the wf_data file FALSE do not read the CI coefficients from disk
RECOMMENDATION:
      

ASCI_SPIN_PURIFY
       Indicates whether or not the ASCI wavefunction should be augmented with missing determinants to ensure a spin-pure state.
TYPE:
       BOOLEAN
DEFAULT:
       FALSE
OPTIONS:
       TRUE augment the wavefunction with determinants to ensure a spin eigenstate FALSE do not augment the wavefunction
RECOMMENDATION:
      

Example 6.48  CASCI calculation for the lowest triplet (Ms=1) state of N2. The adaptive sampling method is employed to tackle a large active space (14e, 32o). The PT2 correction is performed on top of the ASCI wavefunction.

$molecule
   0 1
   N   0.0   0.0   0.0
   N   0.0   0.0   1.8
$end

$rem
   EXCHANGE          hf
   BASIS             cc-pvtz
   CAS_METHOD        1     !1 for CAS-CI, 2 for CASSCF
   CAS_M_S           2     !M_s value*2 (2: triplet)
   ASCI_DIAG         2     !Arma Sparse=0, Davidson=1, Eigen Sparse=2
   CAS_N_ELEC        14    !N_elec
   CAS_N_ORB         32    !N_orb
   CAS_N_ROOTS       1     !N_roots
   CAS_SOLVER        2     !2=ASCI, 1=Olsen, 0=naive
   ASCI_NDETS        28000 !Number of ASCI Determinants
   THRESH            14
   MAX_SCF_CYCLES    400
   SCF_CONVERGENCE   8
   MEM_TOTAL         4000
   MEM_STATIC        1000
   ROSCF             true
   SYMMETRY          false
   SYM_IGNORE        true
   SCF_ALGORITHM     diis_gdm
$end

View output

Example 6.49  ASCI-SCF (using adaptive sapling for CAS) calculation for the ground state of N2 with a large active space (14e, 32o). The PT2 correction is not performed in this case.

$molecule
   0 1
   N   0.0   0.0   0.0
   N   0.0   0.0   1.8
$end

$rem
   EXCHANGE          hf
   BASIS             cc-pvtz
   CAS_METHOD        2  !1 for CAS-CI, 2 for CASSCF
   CAS_M_S           0  !M_s value*2
   ASCI_DIAG         2  !Arma Sparse=0, Davidson=1, Eigen Sparse=2
   CAS_N_ELEC        14 !N_elec
   CAS_N_ORB         32 !N_orb
   CAS_N_ROOTS       1 !N_roots
   CAS_SOLVER        2 !2=ASCI, 1=Olsen, 0=naive
   ASCI_NDETS        28000 !Number of ASCI Determinants
   ASCI_SKIP_PT2     1
   THRESH            14
   MAX_SCF_CYCLES    400
   SCF_CONVERGENCE   6
   MEM_TOTAL         4000
   MEM_STATIC        1000
   SYMMETRY          false
   SYM_IGNORE        true
   SCF_ALGORITHM     diis_gdm
$end

View output