# 7.10.12 Single-Precision Arithmetic in EOM-CC Calculations

(June 30, 2021)

Similar to ground-state CCSD calculations described in Section 6.17, single precision can be used in EOM-CC and EOM-MP2 calculations. 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.

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.

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

Example 7.52  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


View output

Example 7.53  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



View output