Hi, f’’ is positive (c.f. the tables in henke_xxx.cpp and sasaki_xxx.cpp in build/cctbx/eltbx) and f + f’ + i f’’ is used (c.f. cctbx/xray/structure_factors_simple.h: this is not used in production code but all the more optimised production code shall give the same result at that simple implementation). Best wishes, Luc Bourhis

On 8 Oct 2018, at 16:32, [email protected] wrote:

HI Folks,

Question from a colleague - any ideas?

Many thanks Graeme

Begin forwarded message:

From: "Bombardi, Alessandro (DLSLtd,RAL,SCI)" mailto:[email protected]> Subject: cctbx conventions Date: 8 October 2018 at 14:54:10 BST To: "Winter, Graeme (DLSLtd,RAL,LSCI)" mailto:[email protected]>

Hi Graeme,

I am trying to understand the convention used by cctbx, for the anomalous part of the atomic scattering factor. Do you know if it is written as f+f'+if'' with f'' >0

or with

f+f'-if'' with f'' >0

can you help me?

All the best, Alessandro

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I'm pretty sure its a simple addition of the complex numbers: f0 + ( fp + i*fpp ) Unless, of course, you are David Langs, who is one of a camp quite convinced that Bijvoet got it wrong. Cheers, -James On 10/8/2018 7:32 AM, [email protected] wrote:

HI Folks,

Question from a colleague - any ideas?

Many thanks Graeme

Begin forwarded message:

From: "Bombardi, Alessandro (DLSLtd,RAL,SCI)" mailto:[email protected]> Subject: cctbx conventions Date: 8 October 2018 at 14:54:10 BST To: "Winter, Graeme (DLSLtd,RAL,LSCI)" mailto:[email protected]>

Hi Graeme,

I am trying to understand the convention used by cctbx, for the anomalous part of the atomic scattering factor. Do you know if it is written as f+f'+if'' with f'' >0

or with

f+f'-if'' with f'' >0

can you help me?

All the best, Alessandro