[CP2K-user] [CP2K:20080] RESP charges

[Johnson Lam]

Dear all,

I am new user of cp2k and recently embarked on following the tutorial 
of QM/MM study of UREA Zwitterion in 
water(https://www.cp2k.org/exercises:2015_cecam_tutorial:urea). After 
perfoming that QM/MM tutorial, I am currently trying toadapt the related 
input file to compute the RESP of the urea molecule within an isolated 
water box. However, the RRSM is unexpectedly high, reaching 1.10320E+00. 
I performed a separate DFT calculation of the urea molecule without water 
molecules, aiming to obtain the RESP. In this scenario, the RRSM values 
were significantly lower, measuring at 9.00126E-02 and 9.02948E-02 for 
periodic and non-periodic fitting, respectively.
I consulted the paper J. Phys. Chem., 97 , 10269-10280 (1993) and Phys. 
Chem. Chem. Phys., 17 , 14307-14316 (2015); the fitted potential is 
compared with the quantum mechanical (QM) potential. In these studys, only 
the urea molecule is treated at the QM level.* I am curious about 
substantial difference in RRSM values observed between the DFT calculations 
and the QM/MM simulation*. Would someone have idea about that?

Best Regards,
Johnson


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