Muffin tin radius adjustment?
I am trying to analyze some XAFS data on a Sb-Te compound and when I run feff(6) I get errors regarding the coordination number being too small implying the muffin tin radius is too big. In this material the first nearest neighbor bond length is about 3 angstroms (slightly more or less depending on the site). I assume this is related to the cause of the problem. Any suggestions as to how to fix/avoid this sort of problem? feff6 output is pasted below. Interestingly enough, feff8 does not output any error messages and the sum of the paths looks identical (at least at first glance). Is this a false error message or (more likely) has feff8 become more intelligent with regards to defining the muffin tin radius? Feff6 output Calculating potentials and phases... free atom potential and density for atom type 0 free atom potential and density for atom type 1 free atom potential and density for atom type 2 overlapped potential and density for unique potential 0 overlapped potential and density for unique potential 1 overlapped potential and density for unique potential 2 muffin tin radii and interstitial parameters phase shifts for unique potential 0 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. phase shifts for unique potential 1 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. phase shifts for unique potential 2 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. Preparing plane wave scattering amplitudes... nncrit in prcrit 9 Searching for paths... WARNING in PATHS Module: rmax > distance to most distant atom. Some paths may be missing. rmax, ratx 15.50000 15.40291 Rmax 15.5000 keep and heap limits 0.0000000 0.0000000 Preparing neighbor table Feff8 output Calculating potentials ... free atom potential and density for atom type 0 free atom potential and density for atom type 1 free atom potential and density for atom type 2 initial state energy overlapped potential and density for unique potential 0 overlapped potential and density for unique potential 1 overlapped potential and density for unique potential 2 muffin tin radii and interstitial parameters iph, rnrm(iph)*bohr, rmt(iph)*bohr, folp(iph) 0 1.79879E+00 1.71274E+00 1.13279E+00 1 1.81342E+00 1.72495E+00 1.13595E+00 2 1.83703E+00 1.74437E+00 1.14149E+00 mu_old= -0.508 Done with module 1: potentials. Calculating LDOS ... LDOS calculation for specified grid Calculating energy and space dependent l-DOS. It takes time ... potential type 0 potential type 1 potential type 2 Calculating chi and rho... 0 Calculating chi and rho... 1 Calculating chi and rho... 2 Done with LDOS. Calculating cross-section and phases... absorption cross section phase shifts for unique potential 0 phase shifts for unique potential 1 phase shifts for unique potential 2 Done with module 2: cross-section and phases... Done with module 3: FMS. Preparing plane wave scattering amplitudes... Searching for paths... WARNING: rmax > distance to most distant atom. Some paths may be missing. rmax, ratx 1.55000E+01 0.00000E+00 Rmax 15.5000 keep and heap limits 0.0000000 0.0000000 Preparing neighbor table Dr. Paul Fons Senior Researcher National Institute for Advanced Industrial Science & Technology METI Center for Applied Near-Field Optics Research (CANFOR) AIST Central 4, Higashi 1-1-1 Tsukuba, Ibaraki JAPAN 305-8568 tel. +81-298-61-5636 fax. +81-298-61-2939 email: paul-fons@aist.go.jp The lines below are in a Japanese font 〒３０５−８５６８ 茨城県つくば市東１−１−1 つくば中央第４ 近接場光応用工学センター ポール・フォンス主任研究官
Hi Paul, I believe this is a benign error message from Feff6. At least, the results still seem ok to me in the cases where I've seen the 'Hard test in fovrg' messages: The EXAFS and the muffin tin radii look reasonable to me. Getting the benign messages is probably due to my conversion of the Feff6l to mostly double precision, while older Feff6 (and Feff7) had mixed single and double precision. I see that some of the constants in fovrg.f are still single precision. Feff8 uses a completely different algorithm for this (do I actually understand either of them? No I do not!), so it's not surprising that warnings in one would not occur in the other. Can you send an input file that gives this? I have one that also gives fovrg hard tests messages, but I'd like to see if I can figure this out. Thanks, --Matt
Hi Paul, Determining phase shifts is numerically unstable at large nn distances since the bessel functions j_l(kR) are highly oscillatory and sometimes require a more fine grid to match the log derivatives needed to define the phase shifts. Both FEFF6 and FEFF8 allow up to 40 iterations for convergence, but they do use different algorithms and some of the tolerances in FEFF8 were relaxed to prevent the annoying (and generally benign hard test failed errors). Also FEFF8 has the RGRID card to reduce the grid size (e.g., to 0.01) in problem cases, which FEFF6 lacks. If you post a feff.inp, we can also take a look and see if there is a quick fix for FEFF6L. Cheers, John On Tue, 4 Oct 2005, Paul Fons wrote:
I am trying to analyze some XAFS data on a Sb-Te compound and when I run feff(6) I get errors regarding the coordination number being too small implying the muffin tin radius is too big. In this material the first nearest neighbor bond length is about 3 angstroms (slightly more or less depending on the site). I assume this is related to the cause of the problem. Any suggestions as to how to fix/avoid this sort of problem? feff6 output is pasted below. Interestingly enough, feff8 does not output any error messages and the sum of the paths looks identical (at least at first glance). Is this a false error message or (more likely) has feff8 become more intelligent with regards to defining the muffin tin radius?
Feff6 output
Calculating potentials and phases... free atom potential and density for atom type 0 free atom potential and density for atom type 1 free atom potential and density for atom type 2 overlapped potential and density for unique potential 0 overlapped potential and density for unique potential 1 overlapped potential and density for unique potential 2 muffin tin radii and interstitial parameters phase shifts for unique potential 0 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. phase shifts for unique potential 1 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. phase shifts for unique potential 2 Hard tests failed in fovrg. Muffin-tin radius may be too large; coordination number too small. Preparing plane wave scattering amplitudes... nncrit in prcrit 9 Searching for paths... WARNING in PATHS Module: rmax > distance to most distant atom. Some paths may be missing. rmax, ratx 15.50000 15.40291 Rmax 15.5000 keep and heap limits 0.0000000 0.0000000 Preparing neighbor table
Feff8 output
Calculating potentials ... free atom potential and density for atom type 0 free atom potential and density for atom type 1 free atom potential and density for atom type 2 initial state energy overlapped potential and density for unique potential 0 overlapped potential and density for unique potential 1 overlapped potential and density for unique potential 2 muffin tin radii and interstitial parameters iph, rnrm(iph)*bohr, rmt(iph)*bohr, folp(iph) 0 1.79879E+00 1.71274E+00 1.13279E+00 1 1.81342E+00 1.72495E+00 1.13595E+00 2 1.83703E+00 1.74437E+00 1.14149E+00 mu_old= -0.508 Done with module 1: potentials. Calculating LDOS ... LDOS calculation for specified grid Calculating energy and space dependent l-DOS. It takes time ... potential type 0 potential type 1 potential type 2 Calculating chi and rho... 0 Calculating chi and rho... 1 Calculating chi and rho... 2 Done with LDOS. Calculating cross-section and phases... absorption cross section phase shifts for unique potential 0 phase shifts for unique potential 1 phase shifts for unique potential 2 Done with module 2: cross-section and phases... Done with module 3: FMS. Preparing plane wave scattering amplitudes... Searching for paths... WARNING: rmax > distance to most distant atom. Some paths may be missing. rmax, ratx 1.55000E+01 0.00000E+00 Rmax 15.5000 keep and heap limits 0.0000000 0.0000000 Preparing neighbor table
Dr. Paul Fons Senior Researcher National Institute for Advanced Industrial Science & Technology METI Center for Applied Near-Field Optics Research (CANFOR) AIST Central 4, Higashi 1-1-1 Tsukuba, Ibaraki JAPAN 305-8568
tel. +81-298-61-5636 fax. +81-298-61-2939
email: paul-fons@aist.go.jp
The lines below are in a Japanese font
���������ݣ������� ��븩�Ĥ��л��죱�ݣ���1 �Ĥ�������裴 ���ܾ�����ѹ��إ��� �ݡ��롦�ե���Ǥ���洱
participants (3)
-
John J. Rehr -
Matt Newville -
Paul Fons