I would like to get Force constant matrix calculated using iop(7/33=1) from the Gaussian .log file. I guess that they are placed into the last block, perhaps after the NImag=n data. Is it true? If I am searching for the "1\1\GINC-...\Freq" string, can I get the first column of these block? For the last column, can I search for @? What is the terminating character of the force constant matrix?
If you want to take it from the output file, don't look for the condensed results block in the end. The matrix is given in formatted print in the output file. I've done a quick test job and I actually see it printed more than once. Look for the "Force constants in Cartesian coordinates:" block, for example.
An alternative would be to take the checkpoint file, format it and extract the force constants. But you'd have to reformat the matrix yourself in that case. The advantage would be that the force constants are printed with to 9 significant figures there, if you need that. The output file seems to have 6 at most.
In case you do ever want to extract data from the results block, they are all separated by the pipe character "|". It's a real pain to use that block though, because the data is not always labeled (like the Force Constants), and the lines will just break in the middle of it so that you have to be careful to reassemble your results correctly.
Thank you for your answer. Could you please present this input/output? By the way, the force constant matrix belongs to the original (input) coordinates or the transformed ones?
You can use bash command:
cat file.log |sed -n '/coordinates:/,/ Force/p'
or to file
cat *.log |sed -n '/coordinates:/,/ Force/p'>coordinate.txt
Hello. I would suggest to read it from FCHK files instead of LOG files, if you are going to write programs but not just read some numbers by yourself.
The Hessian matrix in Cartesian coordinates start with: "Cartesian Force Constants", which are same to the "Force constants in Cartesian coordinates" in LOG files. They are in "Standard orientation", which is the transformed ones, if you did not use "nosymm". If you do use "nosymm", then those are in original (input) coordinates.
As @Matthias Heger said, you'll have to reformat it, because FCHK just store the numbers but ignore the format. If you know how to use Python, I have written a code to do this:
https://github.com/ruixingw/rxcclib/blob/dev/utils/my/LTMatrix.py
The code comes with enough comments. You just need to read all force constants and store them in a list, and provide the list to LTMatrix class.
Thank you for your answer. The string "Cartesian Force Constants" cannot be found in my .log file. I have attached my .com file (with .txt extension). Should I use further keys to print the force constant matrix? (By the way, I use Gaussian B.01 version under Linux.)
"Cartesian Force Constants" is in FCHK file. For log file, search for "Force constants in Cartesian coordinates".
Thank you. I would like also ask whether iop(7/33=1) always prints the force constant matrix.
In fact, I would like to get the eigenvalues in their original sorting (not in increasing order). Can IOp(7/8) provide them? If so, what does it mean Kxxxxx?
https://www.researchgate.net/post/How_to_calculate_all_the_force_constants_in_Gaussian092
You can access force constant matrix from Gaussian *fchk file. In the fchk file, the force constants are given in lower triangle Cartesian force constant.
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