feat: add PPCG eigenvalue solver implementation

docs/advanced/input_files/input-main.md

@@ -975,7 +975,7 @@
 ### pw_diag_thr
 
 - **Type**: Real
-- **Description**: Only used when you use ks_solver = cg/dav/dav_subspace/bpcg. It indicates the threshold for the first electronic iteration, from the second iteration the pw_diag_thr will be updated automatically. For nscf calculations with planewave basis set, pw_diag_thr should be <= 1e-3.
+- **Description**: Only used when you use ks_solver = cg/dav/dav_subspace/bpcg/ppcg. It indicates the threshold for the first electronic iteration, from the second iteration the pw_diag_thr will be updated automatically. For nscf calculations with planewave basis set, pw_diag_thr should be <= 1e-3.
 - **Default**: 0.01
 
 ### diago_smooth_ethr
@@ -994,8 +994,8 @@
 ### pw_diag_nmax
 
 - **Type**: Integer
-- **Availability**: *basis_type==pw, ks_solver==cg/dav/dav_subspace/bpcg*
-- **Description**: Only useful when you use ks_solver = cg/dav/dav_subspace/bpcg. It indicates the maximal iteration number for cg/david/dav_subspace/bpcg method.
+- **Availability**: *basis_type==pw, ks_solver==cg/dav/dav_subspace/bpcg/ppcg*
+- **Description**: Only useful when you use ks_solver = cg/dav/dav_subspace/bpcg/ppcg. It indicates the maximal iteration number for cg/david/dav_subspace/bpcg/ppcg method.
 - **Default**: 50
 
 ### pw_diag_ndim

docs/advanced/scf/hsolver.md

@@ -4,7 +4,7 @@
 
 Method of explicit solving KS-equation can be chosen by variable "ks_solver" in INPUT file.
 
-When "basis_type = pw", `ks_solver` can be `cg`, `bpcg` or `dav`. The default setting `cg` is recommended, which is band-by-band conjugate gradient diagonalization method. There is a large probability that the use of setting of `dav` , which is block Davidson diagonalization method, can be tried to improve performance.  
+When "basis_type = pw", `ks_solver` can be `cg`, `bpcg`, `ppcg` or `dav`. The default setting `cg` is recommended, which is band-by-band conjugate gradient diagonalization method. There is a large probability that the use of setting of `dav` , which is block Davidson diagonalization method, can be tried to improve performance.  
 
 When "basis_type = lcao", `ks_solver` can be `genelpa` or `scalapack_gvx`. The default setting `genelpa` is recommended, which is based on ELPA (EIGENVALUE SOLVERS FOR PETAFLOP APPLICATIONS) (https://elpa.mpcdf.mpg.de/) and the kernel is auto choosed by GENELPA(https://github.com/pplab/GenELPA), usually faster than the setting of "scalapack_gvx", which is based on ScaLAPACK(Scalable Linear Algebra PACKage)  
 

docs/parameters.yaml

@@ -519,6 +519,7 @@ parameters:
 
       * cg: The conjugate-gradient (CG) method.
       * bpcg: The BPCG method, which is a block-parallel Conjugate Gradient (CG) method, typically exhibits higher acceleration in a GPU environment.
+      * ppcg: The band-by-band projected preconditioned conjugate gradient method, similar to CG but with an alternative convergence strategy.
       * dav: The Davidson algorithm.
       * dav_subspace: The Davidson algorithm without orthogonalization operation, this method is the most recommended for efficiency. `pw_diag_ndim` can be set to 2 for this method.
 
@@ -942,7 +943,7 @@ parameters:
     category: Plane wave related variables
     type: Real
     description: |
-      Only used when you use ks_solver = cg/dav/dav_subspace/bpcg. It indicates the threshold for the first electronic iteration, from the second iteration the pw_diag_thr will be updated automatically. For nscf calculations with planewave basis set, pw_diag_thr should be <= 1e-3.
+      Only used when you use ks_solver = cg/dav/dav_subspace/bpcg/ppcg. It indicates the threshold for the first electronic iteration, from the second iteration the pw_diag_thr will be updated automatically. For nscf calculations with planewave basis set, pw_diag_thr should be <= 1e-3.
     default_value: "0.01"
     unit: ""
     availability: ""
@@ -966,10 +967,10 @@ parameters:
     category: Plane wave related variables
     type: Integer
     description: |
-      Only useful when you use ks_solver = cg/dav/dav_subspace/bpcg. It indicates the maximal iteration number for cg/david/dav_subspace/bpcg method.
+      Only useful when you use ks_solver = cg/dav/dav_subspace/bpcg/ppcg. It indicates the maximal iteration number for cg/david/dav_subspace/bpcg/ppcg method.
     default_value: "50"
     unit: ""
-    availability: "basis_type==pw, ks_solver==cg/dav/dav_subspace/bpcg"
+    availability: "basis_type==pw, ks_solver==cg/dav/dav_subspace/bpcg/ppcg"
   - name: pw_diag_ndim
     category: Plane wave related variables
     type: Integer

source/source_hsolver/CMakeLists.txt

@@ -4,6 +4,7 @@ list(APPEND objects
     diago_david.cpp
     diago_dav_subspace.cpp
     diago_bpcg.cpp
+    diago_ppcg.cpp
     para_linear_transform.cpp
     hsolver_pw.cpp
     hsolver_lcaopw.cpp