yambo 4.4.0 ./configure bug detecting libxc

[wachr]

Dear yambo community,

while compiling yambo, I found that the use of external libxc libraries is hardly possible. After specifyfing the path for libxc (we have libxc 4.2.1 as a module), ./configure gave me the lines:

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checking for libxc... Found external LibXC version=400, (should be 2xx and >= 203)
Compatible external LibXC not found/specified. Internal to be compiled.

It is not a damage, as the internal libxc will be compiled - but I think that this behavior is not intended. Just to make you aware of this.

Kind regards!

[Davide Sangalli]

Dear Christian Wagner,
you are right. For now we have checked the compatibility of yambo with libxc up to version 210.
This is the reason why the yambo does not accept version 4x.

You can try to switch off the check by changing the file config/libxc.m4
Replace line

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AC_LINK_IFELSE($testprog_4x,  [acx_libxc_version=400, acx_libxc_ok=no ], [])

with

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AC_LINK_IFELSE($testprog_4x,  [acx_libxc_version=400, acx_libxc_ok=yes], [])

Then run autoconf.

The library will be accepted, however I fear the compilation or the code will not work properly.

Best,
D.

[wachr]

Dear Davide,

thank you very much!

The library will be accepted, however I fear the compilation or the code will not work properly.

OK, looks as if I should stick to the default. The automatically downloaded libxc is 2.2.3 - the latest is 4.3.4. Does this harm to any calculations using later versions of the libxc, such as QuantumEsppresso + libxc 4. ...?

Thank you!

[Daniele Varsano]

Dear Christian,

Does this harm to any calculations using later versions of the libxc, such as QuantumEsppresso + libxc 4. ...?

Libxc in QE is not the default, by default, it is used the internal xc library. Most common xc functionals (LDA,PBE, even PBE0) were extensively tested in the sense that internal QE-XC and Yambo via LIbxc provided consistent results. I would be surprised if incompatibility arises between different version of Libxc. In any case, now Yambo reports the value of the E_xc that can be directly compared with the QE output. Please report in case you notice something wrong (pay attention to non-linear core-correction, that anyway is better to avoid).

Best,
Daniele

[wachr]

Dear Daniele,

thank you very much! This is an interesting point to look for in case of inconsistencies! (So far, never occured, question was rather academic).

I have some python scripts that read both, qe output (*.nscf.out) and yambo output (report files and qp files). But as long as one uses LDA and GGA flavors, I would also be surprised.

Best!
Christian