Dalton forum

I am interested in trajectory calculations and would therefore like to access the gradient of the potential. According to the user manual I can request for the numerical derivative of the potential using *CCGR and .NUMGD. In the attached file () I used these keywords but did not get any output for the gradient.

Note that for reasons of computational efficiency, I would like to map/fit the potential first before I start running the trajectory calculations. I could obtain the gradient myself by making some displacements and evaluating the potential energy differences. However, I expect that an evaluation in one DALTON run is more efficient and more accurate.

How can I get access to the gradient at a specified configuration using the CCSD level of accuracy? I am interested in the ground state.

UPDATE:
Using *NMDDRV I am able to get the gradient at the HF level. It seems that I cannot get the gradient at the CCSD level because 1DHAM001 integrals are not read().

If you're only interested in the ground state, then you can calculate analytic gradients using CCS, CC2, MP2, CCSD and CCSD(T) models, according to the manual. There is an example input, that you can find in section 22.6 on page 168 of the latest manual, i.e. for the Dalton2018 release, which you can find here https://daltonprogram.org/documentation/. This is the input shown there:

**DALTON INPUT
.DIRECT
.RUN WAVE FUNCTIONS
**INTEGRAL
.DIPLEN
.DEROVL
.DERHAM
**WAVE FUNCTIONS
.CC
*CC INP
.CCSD
*DERIVATIVES
**END OF DALTON INPUT

Thank you for this suggestion. It is much more convenient to use an analytical gradient.