Hi
COULOMB_SR_EPS will result in an atom dependent cutoff. The atomic range is
dependent on the atomic hardness parameter in xTB.
However, I'm not satisfied with the current solution. It is much more stable than
the original (bug) one, but it still leads to arbitrary results when the parameters are
forced to the limits.
Sent: Saturday, September 24, 2022 5:53 PM
To:
cp...@googlegroups.com
Subject: Re: [CP2K:17752] Re: Large discrepancy in xTB results from CP2K vs DFTB+
Hi Jürg,
I would appreciate your insights about the per-element cutoffs. See my previous email. Is it a feature of xTB or CP2K?
Thank you,
Xavier
I went further with the tests today, now varying COULOMB_SR_CUT (see pictures below). Actually, I like the idea of depending neither on COULOMB_SR_CUT nor on system size with COULOMB_SR_EPS = 1e-3, even though the resulting volume is 12.7% underestimated. But I would appreciate your insights on why it behaves like this (for COULOMB_SR_EPS = 1e-3). You talked earlier about per-element cutoffs. Is that it? And if so, are these per-element cutoffs parameters of xTB as published?
[image.png][image.png][image.png]
Thanks,
Xavier
On Tue, Sep 20, 2022 at 5:53 AM Jürg Hutter <
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch>> wrote:
Hi
I can only guess here. The stress tensor might be a weak point of this type of spherical cutoff
implementation of long-ranged forces. Subtle changes of symmetry (size of your computational box,
k-points) together with the cutoff radius might cause changes in the stress tensor.
regards
JH
________________________________________
Sent: Tuesday, September 20, 2022 4:06 AM
To:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>
Subject: Re: [CP2K:17714] Re: Large discrepancy in xTB results from CP2K vs DFTB+
I just tried with GMAX = 75 or 125 for replication 2x1x2 and COULOMB_SR_EPS = 1e-5, same result as above (lower energy than the unit cell and 3x2x3 supercell, lower volume and lower beta angle).
So the problem may not be the Ewald part.
Is there any known issue with small COULOMB_SR_EPS?
I have a funny behavior with COULOMB_SR_EPS though, with the size of the system (replication of the unit cell to supercell). See the figures below.
For COULOMB_SR_EPS = 1e-2 to 1e-4, there is no variation with the system size, which is good. (Naively?)
For COULOMB_SR_EPS >= 1e-5, there is a deviation, but only for the replication 2x1x2 of the supercell. I have checked with denser k-points 2x2x2 but the behavior is the same.
Would that mean that COULOMB_SR_EPS = 1e-4 is the optimal value?
What could explain this behavior for small COULOMB_SR_EPS??
The automatic Ewald? The only difference is the G-space max. Miller index:
1x1x1 supercell -> 45 75 45
2x1x2 supercell -> 75 75 125
3x2x3 supercell -> 125 125 135
Could that be it?
Let me know what you think.
[image.png][image.png][image.png]
Thanks,
Xavier
thank you for the quick tests. It seems to me that the small COULOMB_SR_EPS has the
effect that all cutoff values are determined by COULOMB_SR_CUT (20 bohr).
This is the reason all your results for 10^-5 and smaller are identical.
I will further investigate how to treat the 1/r^3 terms more efficiently, but this
will not have a high priority.
best regards
JH
________________________________________
From:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>> <
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>> on behalf of Xavier Bidault <
jazz...@gmail.com<mailto:
jazz...@gmail.com><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com>>>
Sent: Sunday, September 18, 2022 9:47 PM
On Sun, Sep 18, 2022 at 9:50 AM Xavier Bidault <
jazz...@gmail.com<mailto:
jazz...@gmail.com><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com>><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com>>>> wrote:
Hi Jürg,
A quick test with EPS_DEFAULT of 1e-10 or 1e-11 yields practically the same variable-cell optimization now for bHMX. So that's better, even though I'll have to check it up with a larger panel of values and watch convergence.
What are the default values you chose for these parameters?
COULOMB_SR_EPS : atom dependent range
COULOMB_SR_CUT : maximum range for all atoms
Are they dependent on the (automatic) Ewald parameters?
If I want to modify them, what would be the section in the input file?
Are they "per atom" or global parameters?
Thank you,
Xavier
On Fri, Sep 16, 2022 at 2:53 AM Jürg Hutter <
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch>><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch>>>> wrote:
I have updated the Trunk version with a new patch for xTB. This should now have the
electrostatic energy calculated as originally expected. The long-range 1/r term is
handled by an Ewald sum (using SPME) and the remaining terms with an 1/r^3 contribution
are cut at an atom dependent distance. The strong dependence of this term on the
requested general accuracy (EPS_DEFAULT) should now be gone.
The range (*2) of this interaction is controlled by two keywords
COULOMB_SR_EPS : atom dependent range
COULOMB_SR_CUT : maximum range for all atoms
This neglects the long range character of the 1/r^3 terms that might affect especially the
stress tensor.
I hope this helps to stabilize simulations.
best regards
JH
________________________________________
From:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>> <
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cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>>> on behalf of Magnus Rahm <
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>>>>
Sent: Wednesday, September 7, 2022 2:20 PM
To: cp2k
Subject: Re: [CP2K:17622] Re: Large discrepancy in xTB results from CP2K vs DFTB+
Btw, I can confirm that the energy now converges with EPS_DEFAULT also for the LiO2 system, although the convergence is perhaps a bit slower (=very small EPS_DEFAULT values needed) than what one might have expected (see LiO2-EPS_DEFAULT.pdf). The figure I attached in my previous post was made with EPS_DEFAULT at the default value, if I use 1e-24 I get a bit closer to DFTB+ but still there is a weird slope in the E-V curve (EV-LiO2.pdf).
Furthermore, I had a look at the energy broken down into its different contributions as a function of volume (LiO2-energies-split.pdf), and FWIW it indicates that the electronic energy is responsible for the unexpected slope in the E-V curve (perhaps that was already obvious?).
> Could you remind me how to update CP2K 2022.1 to include this bug fix?
I think the easiest approach is to use Docker (following these instructions:
https://github.com/cp2k/cp2k/tree/master/tools/docker), unless you want to clone the CP2K repo from github and compile from scratch.
Kind regards,
Magnus Rahm
From:
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cp...@googlegroups.com><mailto:
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cp...@googlegroups.com>>> <
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cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
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cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>>> on behalf of Jürg Hutter <
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch>><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch><mailto:
hut...@chem.uzh.ch<mailto:
hut...@chem.uzh.ch>>>>
Sent: Tuesday, September 6, 2022 11:37 AM
To:
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cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
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cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>>
Subject: Re: [CP2K:17614] Re: Large discrepancy in xTB results from CP2K vs DFTB+
Hi
I think I found the problem. This is in fact a bug in CP2K and is related to the damping of
the "short range" part of the Coulomb term. As mentioned before this short range part
is not short range at all, even diverging in periodic systems. We use a damping function
for this term and the radius is taken from the range of the basis function on each atom.
The bug is now, that this range is not a constant but depends on EPS_DEFAULT.
I will work on a solution, but at least the default settings will cause considerable changes
in the energies of periodic systems.
regards
JH
________________________________________
From:
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cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>> <
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>>> on behalf of Magnus Rahm <
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>>>>
On Monday, September 5, 2022 at 12:18:26 PM UTC+2
jazz...@gmail.com<mailto:
jazz...@gmail.com><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com>><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com><mailto:
jazz...@gmail.com<mailto:
jazz...@gmail.com>>> wrote:
I recently run variable-cell optimization of various molecular crystals and I found xTB@CP2K ultra sensitive to EPS_DEFAULT. Tested from 1e-5 to 1e-24 (with EPS_SCF 1e-8), and no convergence happened. I just ended up with EPS_DEFAULT 1e-10 as a "gut" choice. Also, the behavior of xTB@CP2K is doutfull with MD even at ambiant conditions, where the converged volume is barely larget than at 0K. Depending on EPS_DEFAULT, it can even be smaller at ambient T. Weird. The behavior of DFTB2@CP2K is far better.
I found that DFTB+ has other issues. xTB@DFTB+ has no convergence issue, but the recommended variable-cell optimization algorithm has flaws. The unit cell and a supercell does NOT always end up with related lattice parameters. The main issue is that some 90° angles are not preserved with DFTB+ whereas CP2K does (with no symmetry enforced, obviously). Some inconsistencies appears in DFTB+ with a lattice dimensions < 10 angstroms in the unit cell versus > 10 angstroms in the supercell. A proper tight mesh of k-points does not improve. So I'm afraid that xTB@DFTB+ (or DFTB+, actually) cannot be a relevant choice for crystal structure predictions, for instance.
xTB may be unreliable with CP2K and DFTB+, but for the different reasons above. You can check these weird behaviors with your own crystals of interest.
Xavier
From:
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cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>> <
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com><mailto:
cp...@googlegroups.com<mailto:
cp...@googlegroups.com>>>> on behalf of Magnus Rahm <
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com><mailto:
mag...@compulartech.com<mailto:
mag...@compulartech.com>>>>
Sent: Monday, September 5, 2022 8:40 AM
To: cp2k
Subject: [CP2K:17599] Re: Large discrepancy in xTB results from CP2K vs DFTB+
For the record, the problem is the same in CP2K version 2022.1.
On Thursday, September 1, 2022 at 12:48:35 PM UTC+2 Magnus Rahm wrote:
Dear all,
I want to use CP2K (version 8.2, trying to get a more recent version compiled) together with xTB for a crystal containing Li and O. I get strange results already for a simple LiO2 crystal:
* There is a very large discrepancy compared to DFTB+ (version 22.1).
* Mulliken charges tend to be large, meaning that CHECK_ATOMIC_CHARGES stops the SCF. If I turn it off, the system tends to converge systematically to values just outside the "chemical range". Mulliken charges obtained by DFTB+ are significantly smaller (and within "chemical range").
* The energy-volume curve looks strange and very different from DFTB+.
I have tried converging with respect to system size and the EWALD / ALPHA and GMAX parameters, but they have only a marginal impact. I have tried similar calculations for a number of periodic systems. Sometimes I get agreement, sometimes not. I also tried calculations for CO and NO molecules which agree perfectly between CP2K and DFTB+, whereas an artificial LiF molecule does not.
A perhaps related issue was reported in
https://groups.google.com/g/cp2k/c/oFwgGcQuySs but the solutions suggested there did not solve my problem.
I attach input scripts for CP2K and DFTB+, as well as a figure showing the E-V curve for LiO2 obtained with CP2K and DFTB+. I'm new to CP2K, DFTB+ and xTB so I suspect I have made some simple mistake, and any advice is appreciated.
Kind regards,
Magnus Rahm
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