Create README.md

Author: PeizeLin

README.md

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+# LibRI
+
+Read this in other languages: [English](./README.md), [中文](./README.cn.md)
+
+
+## RI technique
+
+Conventional Density functional theory (DFT) methods are not sufficient to properly describe certain types of binding interactions.
+It is often necessary to use higher-level methods like hybrid functionals, random-phase approximation (RPA), GW methods and beyond to accurately treat.
+However, the computational cost of these methods are prohibitively expensive.
+
+For local bases, invoking the resolution-of-the-identity (RI) significantly reduces the storage requirement and the computational cost.
+
+
+## requirements for LibRI
+
+LibRI is a C++ library using RI technique for methods beyond DFT. It is a head-only library.
+
+These are necessary for LibRI:
+- C++ compiler, supported C++14 and OpenMP.
+- MPI library, used for inter-process communication.
+- BLAS and LAPACK libraries, used as backends for Tensor operations.
+  > If Math Kernel Library (MKL) is linked as the BLAS and LAPACK backend, it's recommended to define macro `__MKL_RI` before including any LibRI's header file. Some LibRI's functions will be silently substituted with calls to MKL routines.
+- [cereal](https://uscilab.github.io/cereal/) library, a head-only library for serialization.
+- [LibComm](https://github.com/abacusmodeling/LibComm.git) library, a head-only library for inter-process communication.