Hello,

I'm wondering if anyone can help me here.

I'm performing a rather large $DEL-type optimisation in Gaussian using the "zero" keyword, as given in the example in this tutorial.

My system is much bigger than a water dimer however, and when I input the following into my input file:

$nbo print=0 nbosum $end

$del

zero 2 deloc from 1 to 2 from 2 to 1

$end

My output file gives me this:

Zero delocalization from unit 1 to unit 2

Zero delocalization from unit 2 to unit 1

Deletion of the NBO Fock matrix elements between orbitals:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 41

42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61

62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101

102 103 104

and orbitals:

182 183 184 1851007100810091010101110121013101410151016101710181019102010211022

10231024102510261027102810291030103110321033103410351036103710381039104010411042

10431044104510461047

Deletion of the NBO Fock matrix elements between orbitals:

40 105 106 107 108

and orbitals:

Before terminating the NBO programme. Basically it doesn't seem to be able to delete all the Fock matrix elements.

As can be seen, there is 1047 orbitals in total, and I noticed on the tutorial I linked it has the following line:

"Note that such $DEL-type optimizations are performed by non-analytic derivative methods that are quite time-consuming, hence restricted to a limited number of optimization variables in practical applications."

Are "optimization variables" the Fock matrix elements, and therefore, does my system exceed the limited number of variables for this calculation to be performed? If so, is there a way a round this or is my system simply too big for $DEL-type calculations.

I've used NBO6.0 on the exact same system for standard NBO calculations and it works fine. It's just this $DEL-type calculation that is giving me problems.

Thanks

KTP