Problems with RPBE

[Wan-Lu Li]

Dear CP2K users,

I'm wondering if I implemented RPBE right or not. I compared the inter-molecular interaction of water dimers using B97M_rV and RPBE functionals. But I found that the binding energy difference is quiet large. The energy based on B97M_rV is 5.19 kcal/mol, while RPBE is only 1.65 kcal/mol. I'm sure the B97M_rV result is correct. So why RPBE underestimate the energy quite large. I attach the input for RPBE (one water) here, please help me check it. Thanks in advance!

Best regards,

Wanlu

&FORCE_EVAL
        METHOD QS
        &DFT
                BASIS_SET_FILE_NAME BASIS_MOLOPT
                POTENTIAL_FILE_NAME GTH_POTENTIALS
                &MGRID
                        CUTOFF 1200
                        REL_CUTOFF 60
                &END MGRID
                &QS
                        EPS_DEFAULT 1.0E-12
                &END QS
                &SCF
                   EPS_SCF 1.0E-6 

                   &OT ON
                           MINIMIZER DIIS
                   &END OT
                   &OUTER_SCF ON  
                           MAX_SCF 5
                           EPS_SCF 1.0E-6

                   &END OUTER_SCF
                  &END SCF
                  &XC
                        &XC_FUNCTIONAL
                                &LIBXC
                                        FUNCTIONAL GGA_X_RPBE
                                &END LIBXC

                        &END XC_FUNCTIONAL

                        &XC_GRID
                                XC_DERIV NN50_SMOOTH
                        &END XC_GRID
                 &END XC
                 &POISSON
                         PERIODIC none
                         POISSON_SOLVER wavelet
                 &END POISSON
        &END DFT
        &SUBSYS
                &CELL
                        ABC 20.0 20.0 20.0
                        ALPHA_BETA_GAMMA 90.0 90.0 90.0
                        PERIODIC NONE
                &END CELL
                &COORD

                O   1.350625   0.111469   0.000000
                H   1.680398  -0.373741  -0.758561
                H   1.680398  -0.373741   0.758561
                &END COORD
                &TOPOLOGY
                        &CENTER_COORDINATES
                        &END CENTER_COORDINATES
                &END TOPOLOGY
                &KIND O
                        BASIS_SET TZVP-MOLOPT-GTH
                        POTENTIAL GTH-PBE-q6
                &END KIND
                 &KIND H
                         BASIS_SET TZVP-MOLOPT-GTH
                         POTENTIAL GTH-PBE-q1
                &END KIND

         &END SUBSYS
&END FORCE_EVAL

&GLOBAL
        PROJECT Dimer_SP
        RUN_TYPE Energy
&END GLOBAL

[Thomas Kühne]

Dear Wan-Lu, 

since RPBE just contains a modified exchange enhancement factor to mimic 

rPBE yet still fullfilling the local Oxford-Lieb bound, IMHO you simply missing 

plain conventional PBE correlation. 

Cheers, 

Thomas

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==============================

Thomas D. Kühne

Dynamics of Condensed Matter

Chair of Theoretical Chemistry

University of Paderborn

Warburger Str. 100

D-33098 Paderborn

Germany

tdku...@mail.upb.de

+49/(0)5251/60-5726

[Thomas Kühne]

[Wan-Lu Li]

Dear Thomas,

Thanks a lot. 

Now is it OK for the settings in XC part? Like:

                &XC
                        &XC_FUNCTIONAL PBE

                                &LIBXC
                                        FUNCTIONAL GGA_X_RPBE
                                &END LIBXC
                        &END XC_FUNCTIONAL
                        &XC_GRID
                                XC_DERIV NN50_SMOOTH
                        &END XC_GRID
                 &END XC

 

I still found that the optimized structural parameters are unreasonable, such as a simple molecule CO (the bond length is calculated only to be 0.97 angstrom)

Best,

Wanlu

Thomas Kühne <tku...@gmail.com> 于2019年11月28日周四 上午1:44写道：

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[Patrick Gono]

Dear Wanlu,

Now you are using PBE correlation + PBE exchange (due to the PBE functional specified), and on top of that the RPBE exchange.

Use instead:

                &XC
                        &XC_FUNCTIONAL

                                &LIBXC
                                        FUNCTIONAL GGA_X_RPBE
                                &END LIBXC

                                &LIBXC
                                        FUNCTIONAL GGA_C_PBE
                                &END LIBXC

                        &END XC_FUNCTIONAL
                        &XC_GRID
                                XC_DERIV NN50_SMOOTH
                        &END XC_GRID
                 &END XC

Yours sincerely,

Patrick Gono

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