Hi,
I'm trying to run a EOM-CCSD calculation on a small metal oxide cluster using the input file quoted below. The EOM-CCSD part initially appears to converge fine to finite positive excitation energies but then suddenly all excitation energies go to ~ 0:
Iteration 55 using 191 trial vectors
0.0000000185485 0.1308371004755 3.56026
0.0000000217031 0.1514621903177 4.12150
0.0000000502665 0.1557777882543 4.23893
0.0000001651624 0.1592055635125 4.33221 39.6 95.0
Iteration 56 using 192 trial vectors
0.0000000185310 0.1308371004725 3.56026
0.0000000217483 0.1514621903270 4.12150
0.0000000502447 0.1557777882534 4.23893
0.0000002061116 0.1592055636822 4.33221 37.9 96.4
Iteration 57 using 193 trial vectors
0.0000000206880 0.1308371004792 3.56026
0.0972397023418 0.1512362019195 4.11535
0.0000010404410 0.1514621880161 4.12150
0.0000000509268 0.1557777882525 4.23893 41.7 103.5
Iteration 58 using 195 trial vectors
0.2293048302535 0.0497522482240 1.35383
0.0000000185506 0.1308371004717 3.56026
0.0000000131591 0.1514621903330 4.12150
0.0000000464140 0.1557777882910 4.23893 41.7 101.0
Iteration 59 using 196 trial vectors
0.1291815713422 0.0111206134933 0.30261
0.0000000184843 0.1308371004743 3.56026
0.0000000129946 0.1514621903290 4.12150
0.0000000464518 0.1557777882908 4.23893 39.6 98.6
Iteration 60 using 197 trial vectors
0.0547753241375 0.0017883588845 0.04866
0.0000000184471 0.1308371004725 3.56026
0.0000000128898 0.1514621903422 4.12150
0.0000000464864 0.1557777882977 4.23893 40.2 100.0
Iteration 61 using 198 trial vectors
0.0222281569063 0.0001943932224 0.00529
0.0000000184456 0.1308371004724 3.56026
0.0000000128447 0.1514621903391 4.12150
0.0000000464965 0.1557777882961 4.23893 40.2 100.4
Some steps later they all become essentially zero:
Iteration 100 using 309 trial vectors
0.0000321101923 -0.0000005642338 -0.00002
0.0000157935150 -0.0000001284763 0.00000
0.0000000312833 0.0000000000104 0.00000
0.0001271946947 0.0000012507538 0.00003 81.6 186.7
Could someone please tell me what the problem might be here? This is the input I used:
START tio2_2_clubeomcc
MEMORY 1800 MB
GEOMETRY
Ti 1.5800350 0.0816697 0.0000000
O 0.6579338 -1.4182969 0.0000000
O 0.5150702 0.7437215 -1.2499304
O 0.5150702 0.7437215 1.2499304
Ti -0.8204234 -0.0468890 0.0000000
O -2.4476859 -0.1039269 0.0000000
END
BASIS
* library cc-pvdz
END
SCF
SINGLET
RHF
END
TCE
CCSD
FREEZE CORE ATOMIC
NROOTS 4
END
TASK TCE ENERGY
Thanks in advance,
Martijn
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