Hello
Why might the researcher in the field of computational quantum chemistry to develop the function, for example, from b3lyp to GD3BJ when he wants to calculate some systems, for example first step i.e. geometry optimization, what may introduce that for calculation?
There is an important difference between the functionals you mention. B3LYP is unsuitable to describe covalently non-bonded systems, whereas
GD3BJ was designed to properly treat them: it includes D3 dispersion correction by Grimme.
The question is somewhat unclear.
I will point out that most Density Functional Approximations, including the well-known B3LYP, suffer from some well-known failures. One of them is that they fail to describe long-range non-covalent interactions. Therefore, if your system looks like it will have some non-covalent interactions, your should try to fix it.
You can either increase the amount of %HF exchange in your functional (M062X, for example, is more exchange-rich than B3LYP), use an improved functional (CAM-B3LYP is the immediate option coming from B3LYP, although the B97D family is popular, plenty of options nowadays) or include some semiempirical dispersion corrections (among which the GD3BJ is probably the best known).
Do note that the way you try to fix this issue is important. For example, a long range correction via range-separation in the functional will have a much more physical (and understandable) effect on the description of the system (densities, populations) than a massive increase in exchange tuned via parametrization or a semiempirical correction. Grimme's GD3BJ is very well done, though, and can be trusted for sure.
Well, I hope It helped you a bit, although I have been somewhat shallow. What should definitely NOT be done is describing a system with relevant non-covalent interactions with pure B3LYP. Lets try to avoid that.
Thank you so much Ruben Laplaza for your good and informative answer.
مرحبا استاذ فؤاد
شكرا لك لأهتمامك بالسؤال
اثناء عملي في اطروحة الدكتوراه في بدء الجزء العملي استعمل مشرفي الدالة GD3BJ وقال لتطوير الدالة الهجينة B3LYP
اريد ان اعرف حول الموضوع بشكل اوسع ماهو السبب بدقة
مع التقدير
طبعا لأن الكتابة عربي والدوال انكليزي اصبح التعبير مختلف وهو ان الدالة B3LYP هي المطورة للدالة GD3BJ