Can a GM title be given to someone after he dies? For example can Rashid Nezhmetdinov receive a GM title for his contribution to Chess?
Yes, it is possible. FIDE can award the title of honorary grandmaster, based on a player's past performances and/or other contributions to chess.
The Grandmaster (or GM) title is awarded to players who fit two criterias :
- Their ELO rating is above 2500.
- They have achieved 3 GM norms. A GM norm is achieved when a performance of 2600 is reached at the end of the tournament. Moreover, all tournaments don't qualify for GM norms : there must be at least 3 GMs in attendance with a minimum rating of 2200, the tournament must allow for at least 120 mins of thinking time per match (including increments), there must be a FIDE referee, etc...
The title of International Master (or IM), Women Grandmaster (WGM) and Women Internation Master (WIM) are also obtained through a similar process, though the level required is lower. For instance, the required ELO rating for an IM title is of 2400.
More details can be found in the FIDE handbook, in particular in sections 1.4 though 1.7.
So, to answer your question, the title cannot be given posthumously if the person hasn't achieved these results during their lifetime, no matter how much they contributed to the game of chess. It's hard to believe a dead person would make a GM norm.
There is a small chance that a person did qualify but died before FIDE made it official. Although Umlin gave the standard answer for how to achieve the GM title, there is an exceptions. Winning a championship tournament, such as Senior World or even u18, gives you an automatic GM title. This is to ensure that a GM always wins the tournament. (It would look silly for an untitled player to win such a strong tournament.)