Implement TFCC approach for full vibronic problem

[bsonghao]

d853e4eb54eb0f675845cb19a8d23916a36589f7 manage to implement the approach

[bsonghao]

Here are some preliminary result for one of Neil's two by two models

[bsonghao]

Tasks

• [x] Benchmark TFCC method on difference models
• [x] Test effect on different choice of temperature of the thermal field reference state on a same model
• [ ] calculate physical density matrix for TFCC
• [x] derive initial analytical expression for CC amplitudes of the quadratic models
• [x] Implement the modification of the projection manifold

[bsonghao]

ad5600553253c892faf880a209eb5da848c1a296 implement intial T amplitude for quadratic. Now numerical exact for general single surface quadratic model

[bsonghao]

Benchmark between FCI, TFCC, TFCC with modified projection manifold with the same two by two vibronic model