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14.1 Sorted integrals

If the integrals are stored on disk, immediately after evaluation they are sorted into complete symmetry-packed matrices, so that later program modules that use them can do so as efficiently as possible. As discussed above, it is normally not necessary to call the integral and sorting programs explicitly, but sometimes additional options are desired, and can be specified using the INT command, which should appear after geometry and basis specifications, and before any commands to evaluate an energy.

INT, [[NO]SORT,] [SPRI=value]

SORT, [SPRI=value]

INT,NOSORT;SORT can be used to explicitly separate the integral evaluation and sorting steps, for example to collect separate timing data. With value set to more than 1 in the SPRI option, all the two-electron integrals are printed.

The detailed options for the integral sort can be specified using the AOINT parameter set, using the input form

AOINT, key1=value1, key2=value2, $\dots$

AOINT can be used with or without an explicit INT command.

The following summarizes the possible keys, together with their meaning, and default values.

c_final

Integer specifying the compression algorithm to be used for the final sorted integrals. Possible values are 0 (no compression), 1 (compression using 1, 2, 4 or 8-byte values), 2 (2, 4 or 8 bytes), 4 (4, 8 bytes) and 8. Default: 0

c_sort1

Integer specifying the compression algorithm for the intermediate file during the sort. Default: 0

c_seward

Integer specifying the format of label tagging and compression written by the integral program and read by the sort program. Default: 0

compress

Overall compression; c_final, c_seward and c_sort1 are forced internally to be not less than this parameter. Default: 1

thresh

Real giving the truncation threshold for compression. Default: $0.0$, which means use the integral evaluation threshold (GTHRESH,TWOINT)

io

String specifying how the sorted integrals are written. Possible values are molpro (standard MOLPRO record on file 1) and eaf (Exclusive-access file). eaf is permissible only if the program has been configured for MPP usage, and at present molpro is implemented only for serial execution. molpro is required if the integrals are to be used in a restart job. For maximum efficiency on a parallel machine, eaf should be used, since in that case the integrals are distributed on separate processor-local files.

For backward-compatibility purposes, two convenience commands are also defined: COMPRESS is equivalent to AOINT,COMPRESS=1, and UNCOMPRESS is equivalent to AOINT,COMPRESS=0.

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