[CP2K-user] [CP2K:14133] MIX_CL_TRUNC + ADMM in cp2k development branch

[august... at chem.uzh.ch]

Dear Nicholas,

your XC input looks fine to me, but I have a few remarks. The cutoffs of the truncated Coulomb potential and the long range erf functions are very short. We typically use cutoffs that are around 6 Angstrom, which ensures that results are close enough to a calculation with standard Coulomb potential. Unless you are restarting your calculation from a well converged GGA level calculation, I would refrain from using the SCREEN_ON_INITIAL_P keyword, as the ATOMIC_GUESS starting point might not be good enough for porper screening. Finally, if you are using a range spearated HF potentials, you might want to combine it with a range separated DFT exchange functional as well.

I assume you set up the ADMM section properly and made a sensible choice of primary and auxiliary basis sets. Without your full input file however, this is impossible to say whether there is an issue there.

Hope this helps. Best, 
Augustin

-----cp... at googlegroups.com wrote: -----
To: "cp2k" <cp... at googlegroups.com>
From: "Nicholas Winner" 
Sent by: cp... at googlegroups.com
Date: 10/28/2020 05:14PM
Subject: [CP2K:14133] MIX_CL_TRUNC + ADMM in cp2k development branch

Hello all,

I need to make use of range separated hybrid functionals for periodic systems, so I have pulled the latest development version of cp2k from github which adds this support to admm module (in hfx_admm_utils.F).

To the best of my knowledge, I have implemented it correctly, but the difference in final energy between PBE0 and MIX_CL_TRUNC is ~7 Ha, which seems rather large. When going from GGA -> PBE0 the energy difference <1 Ha. Obviously there should be some change when changing the interaction potential, but this has me considered.

GGA:  ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):             -983.840366364871670 PBE0 : ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):             -983.680119471562080
MIX_CL_TRUNC: ENERGY| Total FORCE_EVAL ( QS ) energy [a.u.]:    -974.290021294811368

Here is the XC section I am using to activate MIX_CL_TRUNC with ADMM. Can someone please sanity check and tell me if this is appropriate? 

                &XC
                         &XC_FUNCTIONAL PBE
                                 &PBE
                                         PARAMETRIZATION ORIG
                                         SCALE_C 1
                                         SCALE_X 0.665 # 1 - alpha - beta
                                 &END PBE
                         &END XC_FUNCTIONAL
                         &HF
                                 FRACTION 1
                                 &SCREENING
                                         EPS_SCHWARZ 1e-07
                                         EPS_SCHWARZ_FORCES 1e-06
                                         SCREEN_ON_INITIAL_P True
                                         SCREEN_P_FORCES True
                                 &END SCREENING
                                 &INTERACTION_POTENTIAL
                                         POTENTIAL_TYPE MIX_CL_TRUNC
                                         CUTOFF_RADIUS 1.8
                                         T_C_G_DATA t_c_g.dat
                                         SCALE_LONGRANGE 0.085 # alpha
                                         SCALE_COULOMB 0.25 # beta
                                         OMEGA 0.94486
                                 &END INTERACTION_POTENTIAL
                                 &LOAD_BALANCE
                                         RANDOMIZE True
                                 &END LOAD_BALANCE
                                 &MEMORY
                                         EPS_STORAGE_SCALING 0.1
                                         MAX_MEMORY 2000
                                 &END MEMORY
                         &END HF
                 &END XC
Best,
Nicholas Winner  
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