Hello every one. I am working on host-guest inclusion complexes via DFT and quantum calculations.
Because tha major interactions found in such systems are non-covalent interactions, i am using dispertion corrections. I optimized all my ligands in DFT/B3LYP-D3 but till now i could not optimize the host which is cucurbit7uril with the same thechnic (since 1 mounth in a 6core machine). I am using both of ORCA and SCM- ADF softwares
Could you suggest me another way to do my calculations with comsuming time coast!!.
Also i want to know if i could use ETS-NOCV, and IQA approches to discribe the system and the interactiions.
Thx for repplying me.
KRID.A
What are the errors ? First, You should try to optimize the system without dispersion functional B3LYP, then take the final geometry and use B3LYP-D3. For non-covalent interactions you may use energy decomposition analysis (EDA).
Dear Adel,
The time taken for this calculations also depends on the size of basis set. Considering the system size of CB7 and guest molecule, I guess 6 core is relatively smaller number of core for the calculation. The usage of D3 again makes it slower.
I will suggest you to optimize the complex with small basis set and b3lyp functional. Then use the optimize structure as a guess structure for medium or larger sized basis set with D3 correction.
Regarding the second question, ETS-NOCV, and IQA can be used in studying the non-covalent intermolecular interactions.
Since you don't have good computational resource, I suggest you use BLYP-D3 or PBE-D3 instead, because in ORCA, when RI is enabled, calculation speed based on pure functional is significantly higher than hybrid functional. For optimization purpose, I highly suggest using these keywords: BLYP def2-SVP D3 gCP(DFT/SVP) opt nopop. In this case, BLYP-D3(BJ) is used with def2-SVP basis set, and meantime, Grimme's gCP method is used to account for BSSE problem and RI-J technique is automatically employed to greatly accelerate calculation.
To characterize weak interaction, the RDG method (also known as NCI method) is quite popular in recent years and should not be ignored, my code Multiwfn (http://sobereva.com/multiwfn) can easily realize this analysis, see Section 4.100.1 of Multiwfn manual for introduction and example (The .molden file generated by orca_2mkl utility of ORCA is supported as input file, but ADF is not supported). Multiwfn also supports a bunch of other very useful weak interaction analysis methods, you can check section 4.A.5 of the manual for a review. IQA may be also useful, but bear in mind IQA analysis is extremely expensive for large system.
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