[Pw_forum] about the logical parameter "use_masses" in IONS card

[lfhuang]

Hello pwscf developers:
    What does the definition of "use_masses" in IONS card (mass-weighted) mean? 
Whose masses are weighted? Is it the weight between the first_image and the last_image,
or just the weight in one configuration according to the masses of all the atoms? When should
we turn on "use_masses" to be .true.?  
    I can't find the answers for these questions in "INPUT_PW" and this forum. Could any kind
one teach me for these? I'd like to appreciate any help very much!
Best Wishes!
Yours Sincerely
L. F. Huang
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L.F.Huang(黄良锋) lfhuang at theory.issp.ac.cn
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Add: Research Laboratory for Computational Materials Sciences,
Instutue of Solid State Physics,the Chinese Academy of Sciences,
P.O.Box 1129, Hefei 230031, P.R.China
Tel: 86-551-5591464-328(office)
Fax: 86-551-5591434
Web: http://theory.issp.ac.cn (website of our theory group)
http://www.issp.ac.cn (website of our institute)
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