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7.10 Coupled-Cluster Excited-State and Open-Shell Methods

7.10.13 Single-Precision Arithmetic in EOM-CC Calculations

(July 14, 2022)

Similar to ground-state CCSD calculations described in Section 6.17, single precision can be used in EOM-CC and EOM-MP2 calculations. 961 Pokhilko P., Epifanovsky E., Krylov A. I.
J. Chem. Theory Comput.
(2018), 14, pp. 4088.
Link
Currently, the following variants of EOM are supported: EE, SF,IP, EA; both in standard and RI/CD implementations, for energies and properties evaluation. If you wish to use single-precision version of EOM, please first read Section 6.17 for basic setup of single-precision coupled-cluster calculation. Here we describe only additional EOM-specific keywords.

Precision selection is controlled by the EOM_SINGLE_PREC keyword: 0 corresponds to double-precision calculation and 1 corresponds to single-precision calculation. EOM-specific convergence criteria are controlled by the same keywords as in the double precision, but the same rule as for CCSD applies: too tight thresholds may cause issues with convergence. The default Davidson threshold 10-5 works well for most cases. 961 Pokhilko P., Epifanovsky E., Krylov A. I.
J. Chem. Theory Comput.
(2018), 14, pp. 4088.
Link

The keyword CC_SP_DM controls calculation of intermediates, density matrices, and S^2 for EOM calculations in the same manner as for CCSD, which is described in Section 6.17.

Calculations of analytical gradients require solving amplitude-response equations, which can be done on single precision as well; this is activated by EOM_ARESP_SINGLE_PREC = 1. For using single precision in calculating response equations for 2PA calculations, use the CC_EOM_2PA_SINGLE_PREC keyword (see also Section 7.10.20.6).

EOM_SINGLE_PREC

EOM_SINGLE_PREC
       Precision selection for EOM-CC/MP2 calculations. Available in CCMAN2 only.
TYPE:
       INTEGER
DEFAULT:
       0 double-precision calculation
OPTIONS:
       1 single-precision calculation 2 single-precision calculation is followed by double-precision clean-up iterations
RECOMMENDATION:
       Do not set too tight convergence criteria when use single precision

CC_EOM_2PA_SINGLE_PREC

CC_EOM_2PA_SINGLE_PREC
       Precision selection for 2PA response equations. Available in CCMAN2 only.
TYPE:
       INTEGER
DEFAULT:
       0 double-precision calculation
OPTIONS:
       1 single-precision calculation
RECOMMENDATION:
       NONE

Note:  Remember to adjust convergence thresholds when using single precision.

Example 7.55  A job evaluating EOM-EA-CCSD energies for formaldehyde anion using single-precision execution combined with CD

$comment
   Formaldehyde anion, single-precision calculation
$end

$molecule
   0 1
   C
   H  1  1.127888
   H  1  1.127888  2  100.546614
$end

$rem
   BASIS                 = cc-pvdz
   METHOD                = ccsd
   CHOLESKY_TOL          = 3
   EA_STATES             = [1,0,0,0]
   CC_REF_PROP           = 1   Compute properties of the CCSD reference
   !SP keywords
   CC_SINGLE_PREC        = 1
   CC_SP_T_CONV          = 4
   CC_SP_E_CONV          = 6
   CC_ERASE_DP_INTEGRALS = 0 ! set 1 to save disk space
   CC_SP_DM              = 1
   !EOM-specific keyword
   EOM_SINGLE_PREC       = 1
$end

Example 7.56  Geometry optimization of a triplet excited state of uracil-water complex in single-precision setup

$molecule
   0 1
   N     0.034130    -.986909    0.000000
   N    -1.173397     .981920    0.000000
   C    -1.218805    -.408164    0.000000
   C    -0.007302    1.702153    0.000000
   C     1.196200    1.107045    0.000000
   C     1.289085    -.345905    0.000000
   O     2.310232    -.996874    0.000000
   O    -2.257041   -1.026495    0.000000
   H     0.049329   -1.997961    0.000000
   H    -2.070598    1.437050    0.000000
   H    -0.125651    2.776484    0.000000
   H     2.111671    1.674079    0.000000
   O     1.747914   -1.338382   -3.040233
   H     2.180817   -1.817552   -2.333676
   H     0.813180   -1.472188   -2.883392
$end

$rem
   JOB_TYPE              = opt
   METHOD                = ccsd
   BASIS                 = cc-pvdz
   CC_STATE_TO_OPT       = [1,1]
   MEM_TOTAL             = 30000
   EE_TRIPLETS           = [1]
   CC_SP_T_CONV          = 4
   CC_SP_E_CONV          = 6
   CC_SINGLE_PREC        = 1
   EOM_SINGLE_PREC       = 1
   CC_SP_DM              = 1
   CC_EOM_PROP           = 1
   EOM_ARESP_SINGLE_PREC = 1
$end