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Similar to ground-state CCSD calculations described in Section 6.15,
single precision can be used in EOM-CC and EOM-MP2 calculations.^{764}
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 6.15 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.^{764}

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 6.15.

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.

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

EOM_ARESP_SINGLE_PREC

Precision selection for amplitude response EOM equations. Available in CCMAN2 only.

TYPE:

INTEGER

DEFAULT:

0
double-precision calculation

OPTIONS:

1
single-precision calculation

RECOMMENDATION:

NONE

$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

$molecule 0 1 N .034130 -.986909 0.000000 N -1.173397 .981920 0.000000 C -1.218805 -.408164 0.000000 C -.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 .049329 -1.997961 0.000000 H -2.070598 1.437050 0.000000 H -.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 basis = cc-pvdz job_type = opt method = ccsd 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