I found very exciting flag in CASINO QMC namely:
If this flag make CASINO QMC linear scaling for sufficiently large molecules? What is the level of error it introduces?MOLGSCREENING (Logical ) Toggle on and off the use of screening in Gaussian basis set calculations of molecules, i.e., the division of space into boxes and the preparation of lists of which Gaussian basis functions have a significant weight in each box. The use of screening should speed up the calculation of large molecules. The screening information can take up a reasonable amount of memory; hence the existence of this keyword.
If it's really linear and error is really small it is very demanding option.
For example such option for "gold standard" method https://www.ncbi.nlm.nih.gov/pubmed/28456208 named DLPNO-CCSD(T) is under development, although some parts are ready.
For DLPNO-CCSD(T) linear regime starts from about 50 carbon atoms. Is it the same for MOLGSCREENING=True?
Best, Vladimir.