add PW_DIAG_NDIM parameter for users to adjust efficiency. (#3998)

Author: haozhihan

source/module_hsolver/diago_dav_subspace.cpp

@@ -72,7 +72,7 @@ void Diago_DavSubspace<T, Device>::diag_once(hamilt::Hamilt<T, Device>* phm_in,
     this->n_band = psi.get_nbands();
 
     // maximum dimension of the reduced basis set
-    this->nbase_x = 2 * this->n_band;
+    this->nbase_x = Diago_DavSubspace::PW_DIAG_NDIM * this->n_band;
 
     psi::Psi<T, Device> basis(1, this->nbase_x, this->dim, &(psi.get_ngk(0)));
     ModuleBase::Memory::record("DAV::basis", this->nbase_x * this->dim * sizeof(T));
@@ -916,4 +916,4 @@ template class Diago_DavSubspace<double, psi::DEVICE_GPU>;
 #endif
 
 #endif
-} // namespace hsolver
+} // namespace hsolver