[CP2K-user] [CP2K:18250] Re: How to speed HF up

[Nicholas Winner]

1. EPS_DEFAULT should be increased to at least 1e-10, maybe 1e-12. It does 
not change the speed of the HF much when you reduce it and creates 
substantial errors.
2. Use a PBE restart file and then set SCREEN_ON_INITIAL_P True. This 
creates very effective screening and rarely causes problems. The initial 
wave function guess needs to be "good" for this approximation to be valid, 
but in my experience it is only invalid when one is very far from 
equilibrium geometries.
3. For your auxiliary basis set, admm-dzp should already be fairly fast, 
but if you want to be more aggressive you can use the older cpFIT basis 
sets. These are less diffuse and will result in quicker HF evaluation.

Other than that there aren't many ways you can squeeze performance other 
than changing your SCF section. Are you noticing that you are taking many 
many SCF steps to converge? Maybe your SCF settings are the problem. I see 
that you are using diagonalization instead of OT. If you must use 
traditional diagonalization, that is okay, but I would suggest trying to 
use some mixing scheme. The default mixing is good for some systems, but in 
general I find broyden mixing is better. Something like

&SCF
            MAX_SCF 100                    !DEFAULT 50
            EPS_SCF 1.0E-5                !DEFAULT 1.0e-5, OT: -6 - -7, FOR 
DIAG CAN BE SMALLER (DEFAULT)
            SCF_GUESS RESTART            !DEFAULT ATOMIC, RESTART FOR 
RESTART
            &DIAGONALIZATION T
            &END DIAGONALIZATION
            &MIXING
                    METHOD BROYDEN_MIXING
                    ALPHA .01
                    BETA .1
             &END
&END SCF


If you include your output it can also help us diagnose what is the problem 
and if there are improvements. 

A side note to Augustine's suggestion. RI will not benefit ADMM. RI can be 
used to improve the speed of HFX with large basis, but since ADMM is a 
small basis the improvements go away.

On Thursday, December 22, 2022 at 4:34:02 AM UTC-8 DMT wrote:

> Hi Augustin,
>
> Thank you for the conformation and advises. I will try RI
>
> Best Regards,
> Dobromir
>
> On Thursday, December 22, 2022 at 1:30:57 PM UTC+2 Augustin Bussy wrote:
>
>> Hi Dobromir,
>>
>> you should keep in mind that HFX is inherently an expensive method 
>> (compared to GGA). From your input file, I would say you are already using 
>> all the tricks I know of:
>>
>>    1. Using the ADMM  method
>>    2. Using a truncated Coulomb operator, although I have to warn you 
>>    about using extreme values such as 2.0 Angstrom (~6 is usually good)
>>    3. Using the largest possible value for MAX_MEMORY
>>    4. Using a loose EPS_SCHWARZ threshold. Here too, 1.0E-6, may be on 
>>    the limit
>>
>> Also, I think that your EPS_DEFAULT value might be dangerously loose, if 
>> you want accurate results. You could optionally try to use the RI-HFX 
>> method by adding the &RI subsection in &HF. Default parameters should be 
>> good enough. There is however no guarantee that it speeds up you particular 
>> calculation.
>>
>> Best,
>> Augustin
>>
>>
>> ------------------------------
>> *From:* cp... at googlegroups.com <cp... at googlegroups.com> on behalf of DMT 
>> <dobro... at gmail.com>
>> *Sent:* Thursday, December 22, 2022 12:02 PM
>> *To:* cp2k <cp... at googlegroups.com>
>> *Subject:* [CP2K:18243] Re: How to speed HF up 
>>  
>> I tried  
>>
>>                 !&PBE_HOLE_T_C_LR
>>                 !    CUTOFF_RADIUS 6.0
>>                 !    SCALE_X 0.25
>>                 !&END PBE_HOLE_T_C_LR
>>
>> in &XF_FUNCTIONAL and
>>
>>             &HF
>>                 FRACTION 0.25
>>                 &SCREENING
>>                     EPS_SCHWARZ 1.0E-6            !DEFAULT 1.0E-10, 
>> TYPICAL -6 - -9, FOR STABLE HFX
>>                     !SCREEN_ON_INITIAL_P T         !FOR A GOOD INITIAL 
>> GUESS FROM A .WFN
>>                 &END SCREENING
>>                 &INTERACTION_POTENTIAL
>>                     POTENTIAL_TYPE TRUNCATED    !TRUNCATED 1/r (Coulomb) 
>> POTENTIAL FOR SPEED UP
>>                     CUTOFF_RADIUS 6.0            !SHOULD BE < HALF THE 
>> CELL
>>                     T_C_G_DATA /home/lsd/cp2k_data/t_c_g.dat     !DATA 
>> FOR THE EVAL OF TRUNCATED GAMMA FUNC
>>                 &END INTERACTION_POTENTIAL
>>
>> in &XC and there is no significant (if any) speed up.
>>
>> I even played with the CUTOFF_RADIUS (values from 2.0 to 6.0) and nothing 
>> changes.
>>
>> Am I missing something ?
>>
>> Best Regards,
>> Dobromir
>>
>> On Tuesday, December 20, 2022 at 8:31:44 PM UTC+2 DMT wrote:
>>
>> Hello, 
>>
>> I have heard that there must be a way to speed HF (for hybrid DFT 
>> methods) up. Can you help me with that ?
>>
>> Best Regards,
>> Dobromir
>>
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>> .
>>
>

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