[CP2K-user] [CP2K:11257] DF2 van der Waals (vdW) and XC functionals

[Patrick Gono]

Dear Ronald,

Thank you so much for your help. What you write makes perfect sense.
> However, I am still stymied by the example, as it seems to include two
> exchanges and two correlations.
> XC_GGA_X_RPW86 includes both exchange and correlations
>

Please, feel free to ignore the leading XC_. Only the _X_ or _C_ in the
middle of the value specify exchange or correlation, respectively. You can
find all the available functionals (be it exchange, correlation, or both)
here:
https://tddft.org/programs/libxc/functionals/

You can run the exact same calculation leaving out the leading XC_ in your
functional specifications. I am not entirely sure why it is like this,
probably some holdover from an older version of LibXC or CP2K?
Nevertheless, I hope this clears up the issue.

Yours sincerely
Patrick Gono

On Tue, 12 Feb 2019 at 18:39, Ronald Cohen <reco... at gmail.com> wrote:

> Dear Patrick Gono,
>
> Thank you so much for your help. What you write makes perfect sense.
> However, I am still stymied by the example, as it seems to include two
> exchanges and two correlations.
> XC_GGA_X_RPW86 includes both exchange and correlations
> and so does VWN.
> So what does the code do? It seems, at least in the energy, to ADD GGA and
> LDA xc (both x and c),
> and that is certainly not what is wanted.
>
> There is also the issue of using pseudopotentials that correspond to the
> xc for the bands.There are limitless combinations of XC possible, but only
> a few are represented in the cp2k pseudopotentials/\
>
> Sincerely,
>
> Ron
>
>
> &XC
>>
> &XC_FUNCTIONAL NO_SHORTCUT
>>
>> &LIBXC T
>>
>> FUNCTIONAL XC_GGA_X_RPW86
>>
>> &END LIBXC
>>
>> &VWN T
>>
>> &END VWN
>>
>> &END XC_FUNCTIONAL &VDW_POTENTIAL
>>
>> POTENTIAL_TYPE NON_LOCAL &NON_LOCAL
>>
>> TYPE LMKLL
>>
>> VERBOSE_OUTPUT T KERNEL_FILE_NAME ./vdW_kernel_table.dat CUTOFF 160
>>
>> &END NON_LOCAL &END VDW_POTENTIAL
>>
>> &END XC
>>
> ---
> Ron Cohen
> reco... at gmail.com
> skypename: ronaldcohen
> twitter: @recohen3
>
>
>
>
> On Feb 12, 2019, at 6:12 PM, Patrick Gono <patric... at gmail.com> wrote:
>
> Dear Ronald,
>
> it is true that documentation can be sparse. I suggest following the
> articles cited in the manual for more information.
>
> I note some related problems with the documentation. I find examples like
>> for LIBXC:
>>
>> FUNCTIONAL XC_MGGA_X_M06_L XC_MGGA_C_M06_L
>>
>> but the docs at
>>
>> say
>>
>>    - FUNCTIONAL
>>    <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/XC/XC_FUNCTIONAL/LIBXC.html#list_FUNCTIONAL>
>>    - This keyword cannot be repeated and it expects precisely one word.
>>
>> Yet there are "two words"
>>
>> and including VWN afterwards also seems like more than one functional, as
>> I said above.
>>
>
> In older versions (prior to 6.1), the FUNCTIONAL keyword accepted a list
> of words. In the newest version (6.1), this keyword only accepts a single
> word. Note, however, that the section &LIBXC can be repeated. So, instead
> of:
>
> &LIBXC
>   FUNCTIONAL XC_MGGA_X_M06_L XC_MGGA_C_M06_L
> &END LIBXC
>
> you can do:
>
> &LIBXC
>   FUNCTIONAL XC_MGGA_X_M06_L
> &END LIBXC
> &LIBXC
>   FUNCTIONAL XC_MGGA_C_M06_L
> &END LIBXC
>
> You can also mix different correlation or exchange functionals, like so:
>
> &XC_FUNCTIONAL
>   &LIBXC
>     FUNCTIONAL  XC_GGA_X_RPW86
>   &END LIBXC
>   &LIBXC
>     FUNCTIONAL  GGA_C_PBE
>   &END LIBX
> &END XC_FUNCTIONAL
> &vdW_POTENTIAL
>   DISPERSION_FUNCTIONAL NON_LOCAL
>   &NON_LOCAL
>     TYPE RVV10
>     PARAMETERS  9.3   0.0093
>     KERNEL_FILE_NAME  ./rVV10_kernel_table.dat
>     CUTOFF      400
>   &END NON_LOCAL
> &END vdW_POTENTIAL
>
>
>
> where I used RPW86 exchange and PBE correlation. The reason behind that is
> that I am trying to use the (modified) rVV10 nonlocal van der Waals
> functional. In the original paper:
> https://journals.aps.org/prb/abstract/10.1103/PhysRevB.87.041108 the
> authors define the total exchange-correlation as:
> XC_rVV10 = X_RPW86 + C_PW_LDA + C_non-local_vdW
>
> However, in later work it was found that the non-local vdW correction from
> the rVV10 works quite well with other combinations of correlation and
> exchange functionals. Hence, I am now using
> XC_rVV10 = X_RPW86 + C_PBE + C_non-local_vdW
> with a specific choice of the b parameter in the vdW correction.
>
> What I am trying to say is that you can mix and match the non-local vdW
> correction with different exchanges and correlations. The specific choice
> will always depend on the system you are trying to study. There are many
> papers testing and comparing various combinations, such as this one
> https://pubs.acs.org/doi/10.1021/ct4003527 where the VV10 corrections is
> added to various exchanges and correlations.
>
> In your input file you use the Lee-Murray-Kong-Lundqvist-Langreth (LMKLL)
> nonlocal van der Waals density functional (via the keyword TYPE LMKLL). If
> you look up the relevant publication, you will find what correlation and
> exchange functional it is supposed to be used with. You may also find
> benchmark papers that use this non-local correction on top of
> other-than-originally-intended exchange and correlation functionals. This
> allows one to choose the best combination for the system at hand (large
> system vs small; periodic vs isolated; metals vs semiconductors vs small
> molecules; etc.).
>
> Hope this helps.
> Yours sincerely,
> Patrick Gono
>
> On Tue, 12 Feb 2019 at 15:02, Ronald Cohen <reco... at gmail.com> wrote:
>
>> I am quite confused about the (lack of) documentation for the XC
>> functionals and non-local vdW. I find examples such as:
>>
>> &XC
>>
>> &XC_FUNCTIONAL NO_SHORTCUT
>>
>> &LIBXC T
>>
>> FUNCTIONAL XC_GGA_X_RPW86
>>
>> &END LIBXC
>>
>> &VWN T
>>
>> &END VWN
>>
>> &END XC_FUNCTIONAL &VDW_POTENTIAL
>>
>> POTENTIAL_TYPE NON_LOCAL &NON_LOCAL
>>
>> TYPE LMKLL
>>
>> VERBOSE_OUTPUT T KERNEL_FILE_NAME ./vdW_kernel_table.dat CUTOFF 160
>>
>> &END NON_LOCAL &END VDW_POTENTIAL
>>
>> &END XC
>>
>>
>> (from
>> http://archer.ac.uk/training/course-material/2014/08/CP2K/Slides/NSCCS_2014_Sanliang_Ling.pdf
>>  )
>>
>>
>> and similar even in the regtests.
>>
>> This seems to call both XC_GGA_X_RPW86 and VWN (lda) .
>>
>> What does it mean to call two different xc potentials in cp2k, and why
>> would one do it?
>>
>> Tracing this in the code is not so easy either.
>>
>>
>> Ins eom docs it seems to suggest that LDA only should be used for
>> correlation. Is that because GGA is included
>>
>> in the vDW function in cp2k? Also there is the question which
>> pseudopotentials to use.
>>
>>
>> It seems to me that  XC_GGA_X_RPW86 is correct without the VMN, and this
>> would correapond to what is done for DF2 in
>>
>> quantum espresso it seems.
>>
>>
>> I note some related problems with the documentation. I find examples like
>> for LIBXC:
>>
>> FUNCTIONAL XC_MGGA_X_M06_L XC_MGGA_C_M06_L
>>
>> but the docs at
>>
>> say
>>
>>    - FUNCTIONAL
>>    <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/XC/XC_FUNCTIONAL/LIBXC.html#list_FUNCTIONAL>
>>    - This keyword cannot be repeated and it expects precisely one word.
>>
>> Yet there are "two words"
>>
>> and including VWN afterwards also seems like more than one functional, as
>> I said above.
>>
>>
>> Thank you!
>>
>>
>> Ronald Cohen
>>
>>
>>
>>
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