# CCSD(T) Convergence problem

Michelle Coote mcoote at rsc.anu.edu.au
Thu Aug 28 04:29:35 BST 2003

```Hi
I have a URCCSD(T) single point calculation for which the SCF
convergences to a sensible number and the "energy" part of the CCSD(T)
job converges but the DEN1 is stuck (see output below). I end up with a
convergence failure and an RHF and CCSD number, but no CCSD(T).
What does a stuck DEN1 mean, and can anyone suggest tricks for getting
my job to converge?
Thanks,
Michelle Coote
mcoote at rsc.anu.edu.au

-------------
ITER.       NORM       CORR.ENERGY   TOTAL ENERGY   ENERGY CHANGE
DEN1      VAR(S)    VAR(P)  DIIS     TIME
1      1.43797667    -1.13425986 -1066.13719175    -1.13425986
-0.03768000  0.11D-01  0.85D-02  0  0  3728.05
2      1.47481943    -1.16628448 -1066.16921637    -0.03202462
-0.00405097  0.81D-03  0.13D-02  0  0  7236.58
3      1.49041190    -1.17322760 -1066.17615949    -0.00694312
-0.00090392  0.63D-03  0.20D-03  1  1 10782.82
4      1.50612640    -1.17935807 -1066.18228996    -0.00613047
-0.00017929  0.22D-03  0.48D-04  2  2 14343.98
5      1.51335389    -1.18023923 -1066.18317111    -0.00088115
-0.00006712  0.18D-03  0.79D-05  3  3 17927.40
6      1.52082912    -1.18041174 -1066.18334362    -0.00017251
-0.00003707  0.12D-03  0.45D-05  4  4 21520.83
7      1.52807986    -1.18062411 -1066.18355600    -0.00021237
-0.00002910  0.10D-03  0.29D-05  5  5 25098.47
8      1.53485780    -1.18073303 -1066.18366492    -0.00010892
-0.00002434  0.87D-04  0.27D-05  6  6 28685.18
9      1.55305825    -1.18093969 -1066.18387158    -0.00020666
-0.00001875  0.68D-04  0.19D-05  6  1 32256.12
10      1.57151351    -1.18106354 -1066.18399543    -0.00012385
-0.00001537  0.55D-04  0.18D-05  6  2 35806.83
11      1.60332409    -1.18123513 -1066.18416702    -0.00017159
-0.00001241  0.43D-04  0.12D-05  6  3 39357.08
12      1.62097461    -1.18130993 -1066.18424182    -0.00007480
-0.00001090  0.37D-04  0.12D-05  6  4 42886.48
13      1.67147427    -1.18149541 -1066.18442730    -0.00018548
-0.00000840  0.27D-04  0.84D-06  6  5 46423.77
14      1.71257357    -1.18158011 -1066.18451199    -0.00008469
-0.00000661  0.20D-04  0.69D-06  6  6 49961.05
15      1.72256811    -1.18159570 -1066.18452759    -0.00001559
-0.00000634  0.19D-04  0.69D-06  6  5 53503.92
16      1.72426229    -1.18159835 -1066.18453024    -0.00000265
-0.00000630  0.19D-04  0.69D-06  6  5 57056.48
17      1.72541147    -1.18160054 -1066.18453243    -0.00000219
-0.00000628  0.19D-04  0.69D-06  6  5 60567.83
18      1.72593983    -1.18160151 -1066.18453340    -0.00000097
-0.00000627  0.19D-04  0.69D-06  6  5 64005.27
19      1.72625200    -1.18160213 -1066.18453402    -0.00000061
-0.00000626  0.19D-04  0.69D-06  6  5 67451.33
20      1.72642287    -1.18160246 -1066.18453435    -0.00000033
-0.00000626  0.19D-04  0.69D-06  6  5 70938.83
21      1.72652083    -1.18160266 -1066.18453455    -0.00000020
-0.00000626  0.19D-04  0.69D-06  6  5 74501.07
22      1.72657662    -1.18160277 -1066.18453466    -0.00000011
-0.00000625  0.19D-04  0.69D-06  6  5 78047.00
23      1.72660866    -1.18160283 -1066.18453472    -0.00000006
-0.00000625  0.19D-04  0.69D-06  6  5 81590.15
24      1.72662709    -1.18160287 -1066.18453476    -0.00000004
-0.00000625  0.19D-04  0.69D-06  6  5 85134.32
25      1.72663771    -1.18160289 -1066.18453478    -0.00000002
-0.00000625  0.19D-04  0.69D-06  6  5 88700.47
26      1.72664385    -1.18160290 -1066.18453479    -0.00000001
-0.00000625  0.19D-04  0.69D-06  6  5 92262.38
27      1.72664739    -1.18160291 -1066.18453480    -0.00000001
-0.00000625  0.19D-04  0.69D-06  6  5 95815.25
28      1.72664944    -1.18160291 -1066.18453480     0.00000000
-0.00000625  0.19D-04  0.69D-06  6  5 99364.35
29      1.72665062    -1.18160292 -1066.18453481     0.00000000
-0.00000625  0.19D-04  0.69D-06  6  5102910.35

Norm of t1 vector:      0.23266288      S-energy:    -0.00005399
T1 diagnostic (old):  0.04922978       T1 diagnostic (new):  0.04870682
Norm of t2 vector:      0.49398774      P-energy:    -1.18154892
Alpha-Beta:  -0.91901611
Alpha-Alpha: -0.13415374
Beta-Beta:   -0.12837908

?CONVERGENCE NOT REACHED AFTER MAX. ITERATIONS

Spin contamination <S**2-Sz**2-Sz>     0.00034024

```