This question is regarding Gaussian Computational software package. I have a system where one product forms from one conformational arrangement of molecular intermediate (conformational minimum) and another product forms from a second conformational arrangement of the same molecular intermediate (another conformational minimum). These two arrangements can be interconverted via a rotation about a single bond. In order to investigate the subsequent TS from each pathway, I also need to find the pathway that interconverts the two conformers. How can I use Gaussian to find the rotational transition state that converts these two conformations? I have tried QST2 method using both conformers as input but did not work; I also tried doing a scan along the rotation about the single bond and do a subsequent TS search from the scan maxima but to no avail. Any other methods that I can use to find rotational transition states? I imagine the PES to be very flat, how can I improve my input for tighter convergence?
Any suggestions are welcome! thanks!
%nproc=4
# wB97XD/aug-cc-pVDZ OPT=(QST3,MaxCycle=200,VeryTight) Freq Integral=(Grid=UltraFine,Acc2e=12) NoSymm
reactants like structure put anti
0 1
O 3.05301100 -0.03819300 -0.93547000
C 3.74932000 -0.42248000 0.25978200
H 4.52693000 -1.15904500 0.00662400
H 4.23458900 0.45904200 0.70646300
H 3.68002100 0.32056700 -1.56778500
C 2.74453500 -1.01805700 1.22311900
H 2.25877500 -1.89770800 0.78260100
H 3.25513200 -1.32727100 2.14402900
H 1.97171600 -0.28504000 1.48595000
product like structure put gau1
0 1
O 2.85532200 -0.65489600 -0.89682300
C 3.05319500 -0.89419300 0.50308500
H 2.04381800 -1.02380400 0.91271600
H 3.59693400 -1.84138200 0.63831300
H 3.70837700 -0.49806500 -1.31065100
C 3.76818100 0.25370900 1.19235000
H 3.20415200 1.18689700 1.07052400
H 3.87048700 0.04260100 2.26516500
H 4.77855200 0.39408500 0.78057000
TS like structure put anti
0 1
O 3.05318100 0.21532400 -0.89446800
C 3.45120300 -0.76933200 0.07496600
H 3.09502500 -1.74567500 -0.28365400
H 4.54820300 -0.81269200 0.12646600
H 3.82555300 0.64765200 -1.26039400
C 2.86174600 -0.45603300 1.43691100
H 1.76528400 -0.43991300 1.39366000
H 3.16450300 -1.22863200 2.15651700
H 3.21117200 0.51867800 1.80024000
Kindly try this input for Ethanol. It coverged.
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