MOLPRO

29 LOCAL CORRELATION TREATMENTS 206
(T1)
(T1C)
(TF)
(TA)
T0 plus one perturbative update of the triples amplitudes. If the accuracy of T0 is
insufficient (very rarely the case!), this can be used to improve the accuracy. The
computational cost is at least twice as large as for T0. In contrast to T0, the triples
amplitudes must be stored on disk, which can be a bottleneck in calculations for
large molecules. Also the memory requirements are substantially larger than for
T0.
As T1, but a caching algorithm is used which avoids the simultaneous storage of all
triples amplitudes on disk (as is the case for (T1) or (TF)). Hence, T1C requires
less disk space but more CPU-time than T1. The more disk space is made available
for the caching algorithm (using the T1DISK option on the local card, see below),
the less CPU time is used.
Full iterative triples calculation. With full domains and without weak pair approximations
this gives the same result as a canonical (T) calculation. Typically, 3-5
iterations are needed, and therefore the computational effort is 2-3 times larger
than for (T1). The disk and memory requirements are the same as for T1. The T0
energy is also computed and printed. TFULL and FULL are aliases for TF.
As TF, but the T1 energy is also computed. Since the first iteration is different for
T1, the convergence of the triples iterations is slightly different with TF and TA
(TF being somewhat faster in most cases). TALL and ALL are aliases for TA.
Density fitting can be invoked by prepending the command name by DF-, e.g. DF-LMP2,
DF-LCCSD(T0) etc. In density fitting calculations an additional auxiliary basis set is needed.
Details about choosing such basis sets and other options for density fitting are described in
sections 29.10 and 15.
The general input for local coupled LMP2 or coupled cluster calculations is:
LMP2,options
LCCSD,options
LCCSD(T0),options
Local MP2 calculation
Local CCSD calculation
Local CCSD(T0) calculation
The same options as on the command line can also be given on subsequent LOCAL and MULTP
directives. Instead of using the MULTP directive, the MULTP option on the command line can
also be used.
In the following, we will first give a summary of all options and directives. These will be
described in more detail in the subsequent sections. For new users it is recommended to read
section 29.9 at the end of this chapter before starting calculations.
29.3 Summary of options
Many options can be specified on the command line. For all options appropriate default values
are set, and so these options must usually be modified only for special purposes. For convenience
and historical reasons, alias names are available for various options, which often correspond to
the variable name used in the program. Table 14 summarizes the options, aliases and default
values. In the following, the parameters will be described in more detail.