12 Performance of sapt2012

The computational cost of sapt2012 calculations depends on the system size in the following way. The integral/SCF calculation time scales at most as (o + v)4, with a somewhat lower power expected for large systems. When the AO-based algorithm for the four-virtual diagram in CC is used (which is the default in sapt2012.2 when atmol1024 or molpro are used as the integral/SCF program), the transformation step scales as o(o + v)4 and the CCSD step as o2(o + v)4. Otherwise, the scalings of the transformation and CCSD steps are proportional to v(o + v)4 and o2v4, respectively. Finally, the scaling of the perturbation theory code strongly depends on the required level of theory: o3v2 for SAPT(0), o2v3 for SAPT2, and o3v4 for the full SAPT. For a general orientation, Table 2 contains timings from an Opteron 252 Linux system, obtained with the sapt2012 suite compiled in the 64-bit mode with Portland pgf90 compiler. The examples chosen are described in Sec. 13 under the labels ArHF_DCBS, CO2D_MCBS, and C6H6_H2O_DCBS. For the sake of completeness, the amounts of memory and disk space required in each calculation are also reported (see Sec. 10.7 for a general discussion of these two issues). The memory requirements of the integral/SCF calculations are omitted because they are negligible compared to the other steps. Table 2 is restricted to regular SAPT calculations on a single core. See Ref. 57 for a detailed analysis of the SAPT(DFT) performance and Ref. 9 for a discussion of the parallel SAPT scaling.

Table 2: Wall-clock execution times and memory/disk requirements of different parts of the sapt2012 suite on the Opteron 252 Linux system. The integral/SCF package used is atmol1024.

system Ar-HF (CO2)2 C6H6-H2O

occupied orbitals (A/B) 9/5 11/11 21/5
DCBS size 86 200 262
MC+BS size - 149 -

integral/SCF time 21 s 13 min 53 min
transformation time 15 s 21 min 53 min
CC time 128 s 32 min 16 h 25 min
sapt.x time 84 s 41 min 8 h 9 min

transformation memorya 5.8 Mwords 40 Mwords 380 Mwords
CC memory 2.3 Mwords 11 Mwords 112 Mwords
sapt.x memory 3.0 Mwords 12 Mwords 128 Mwords

integral/SCF disk 42 MB 1.1 GB 7.8 GB
transformation disk 138 MB 1.9 GB 17 GB
CC disk 300 MB 4.8 GB 38 GB
sapt.x disk 268 MB 2.0 GB 23 GB

aMemory amount required for the fastest ’in core’ algorithm is given. tran can also run is significantly smaller memory at the expense of execution time.