There are now so many books on computational chemistry, it becomes a question about which one to read, and then secondly, how to access it.
Below are links to the PDFs of books through their official publisher website.
To download, click on the Wiley 'download full book' or the SpringerLink.
Practical Aspects of Computational Chemistry I, Jerzy LeszczynskiManoj K. Shukla
https://link.springer.com/book/10.1007%2F978-94-007-0919-5
Practical Aspects of Computational Chemistry II, Jerzy LeszczynskiManoj K. Shukla
https://link.springer.com/book/10.1007%2F978-94-007-0923-2
Quantum Computational Chemistry, Taku Onishi
https://link.springer.com/book/10.1007%2F978-981-10-5933-9
Density Functional Theory: A Practical Introduction, David S. Sholl Janice A. Steckel
https://onlinelibrary.wiley.com/doi/book/10.1002/9780470447710
Computational Organic Chemistry, Steven M. Bachrach
https://onlinelibrary.wiley.com/doi/book/10.1002/9780470148136
Computational Chemistry, Introduction to the Theory and Applications of Molecular and Quantum Mechanics, Lewars, Errol G.
https://www.springer.com/gp/book/9789048138616