I am a beginner in DFT. Please suggest me some good material to understand the basics.
Assuming you are interested in pursuing plane-wave periodic DFT, there is a clear best answer in my opinion and that's "Density Functional Theory: A Practical Introduction" by Sholl and Steckel. For a relatively complex topic, they truly manage to accomplish the goal of making this a practical introduction. As they say in the intro, "you don't need to learn how to build a car to learn how to drive from Point A to Point B", and I think that mentality helps a lot with getting started with DFT. It still has enough detail to make it not overly superficial though.
If you're using VASP, I also recommend "Modeling materials using density functional theory" by Kitchin. It's a useful hands-on resource for learning how to use VASP, particularly through the useful program the Atomic Simulation Environment (ASE).
I think to answer the question, one needs to ask another, what part of DFT?
The world of research around quantum chemistry (DFT) but also say coupled cluster simulations or Møller Plesset perturbations can be broken into four main groups:
- method developers
- basis set developers
- code developers
To develop methods or basis sets, you should have a deep understanding of the underlying mathematics. To use it you can be "just a user" depending on what you wish to achieve. If you develop codes, understanding the mathematics surely helps, but you could equally take published materials as given. Typically there are overlaps - and people who are capable of developing methods and basis sets have a deeper understanding that allows them to be "better" users.
Now I am going to assume you mainly want to use DFT:
I studied maths before I ended up working with computational chemistry (and since have been doing "other" things). At the time, "we" had Gaussian at the university. While it has its quirks/troubles it is widely known. And for all the faults present in Gaussian (e.g. lack of stability), the book "Exploring Chemistry with Electronic Structure Methods, James B. Foresman, AEleen Frisch, Gaussian, Inc Gaussian, Inc., 1996" is an excellent basic introduction to the subject. (This is the 2nd edition and many computer related observations are outdated. However there is a newer revision.)
Having said that, I would highly recommend the use of ORCA for quantum chemistry calculations. Besides being more stable, the output is significantly more user friendly. (And I moved to ORCA in subsequent work, some of which would not have been possible without ORCA.)
A more general and in depth book on the subject would be: "Essentials of Computational Chemistry: Theories and Models, Christopher J. Cramer, Wiley, 2004"
A colleague's suggestion at some point: "Introduction to Computational Chemistry, Introduction to Computational Chemistry, Frank Jensen, John Wiley & Sons, 2013" This book deals less with the "hands on" of using computational chemistry methods, but delves into the depths of the key underlying theory. If you intend to understand the underlying mathematics better, this would be surely an interesting book to read.
And finally, my favourite Quantum Chemistry Software comes with extensive documentation and tutorials, it is called ORCA. If you are interested in the details of the implementation, the ORCA manual is ever expanding. "ORCA - An abinitio, DFT and semiempirical SCF-MO package, Frank Neese, Frank Wennmohs, and many others" It is available from the ORCA forum, though google will turn up an older version: https://orcaforum.kofo.mpg.de/app.php/portal
And just for using ORCA, the ORCA Input Library, which is an independent site by a researcher who worked with the developers, is highly recommended too: https://sites.google.com/site/orcainputlibrary/