LINQ to Entities does not recognize the method ,and this method cannot be translated into a store expression

I have following code which get all data using EF and then try converting them to Model as below.

var patients = allpatients.Select(p => CreatePatient(p));

    public Patient CreatePatient(PATIENT p)
        {
            Patient patient = new Patient();

            patient.FIRSTNAME = p.FIRSTNAME;
            patient.MIDDLENAME = p.MIDDLENAME;
            patient.SURNAME = p.SURNAME;

            return patient;
        }

But getting this error

"LINQ to Entities does not recognize the method 'Model.Patient CreatePatient(Repository.PATIENT)' method, and this method cannot be translated into a store expression."