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 AObased algorithm for the fourvirtual 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 o^{2}(o + v)^{4}. Otherwise, the scalings of the transformation and CCSD steps are proportional to v(o + v)^{4} and o^{2}v^{4}, respectively. Finally, the scaling of the perturbation theory code strongly depends on the required level of theory: o^{3}v^{2} for SAPT(0), o^{2}v^{3} for SAPT2, and o^{3}v^{4} 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 64bit 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.




system  ArHF  (CO_{2})_{2}  C_{6}H_{6}H_{2}O 




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 memory^{a}  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 




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