Hello,

I am doing many calculations with an ECP / basis set combination which came without an auxiliary basis for use with RI-J approximation.

The calculations work well, and I would like to move to larger systems, thus I need the large speed advantage this provides.

How does one go about constructing an auxbasis? Is starting with the normal basis and optimizing it to minimize the total energy a sensible procedure? How do I decide how many basis vectors to include? Should I optimize both the exponents and contractions simultaneously, or one at a time? Will varying the auxbasis to minimize the total energy, ensure that the calculations give the result closest to that obtained without the RI-J approximation?

I am attempting to use 'relax' with the following settings in 'control': (If I am going about this wrongly please advise)

In 'control' I set:

$basis file=basis

$jbas file=auxbasis

$optimize

internal off

cartesian off

global off

basis on logarithm

In the file 'auxbasis' I set:

....

$jbas

*

#...

*

3 s expopt contopt

7.7447900000 -0.26903500000

6.7188320000 0.60715300000

2.7444700000 -1.2912950000

1 s expopt contopt

0.65511600000 1.0000000000

Many thanks in advance for sharing your advice and experience?